权利要求

PRODUCTION OF POLYCHLORINATED PYRIDINE MIXTURES BY LIQUID PHASE CHLORINATION OF BETA-PICOLINE OR BETA-PICOLINE HYDROCHLORIDE

Background of the Invention Field of the Invention

The present invention relates to preparation of polychlorinated pyridine mixtures by direct liquid phase chlorination of beta-picoline or beta-picoline hydrochloride. Typical of the products produced are 2,3,6 trichloro- and 2,3,5,6 tetrachloropyridine; and 3-σhloro-, 5-chloro-, 6-chloro-, 2,6-dichloro-, 5,6-dichloro- and 2,5, 6-trichloro-3-trichloromethyl pyridine. These products have utility, for example, as intermediates for herbicides and insecticides. A further aspect of the present invention relates to further chlorination of mixtures rich in 2-chloro- and 6-σhloro-3-trichloromethyl pyridine to form 2,6-dichloro-3-trichloromethyl pyridine and/or 2,3,6-trichloro pyridine, and the further chlorination of mixtures rich in 5-chloro-3-trichloromethyl pyridine and 5,6-dichloro-3-trichloromethyl pyridine to form 2,5,6-trichloro-3-trichloromethyl pyridine and/or 2,3,5,6-tetrachloro pyridine. Description of the Prior Art The utility of 2,3,5,6 tetrachloropyridine as an intermediate to insecticidal compositions is set forth in Dietsche et al U.S. Patent No. 4,256,894. The conversion of 2,3,6 trichloropyridine to the desirable 2,3,5,6 tetrachloropyridine by liquid phase ferric chloride catalyzed chlorination is also taught by Dietsche et al in U.S. Patent No. 4,256,894.

To the best of applicants' knowledge there is no known process for liquid phase chlorination of betapicoline or beta-picoline hydrochloride to yield the valuable chlorinated intermediates 2-chloro-, 5-chloro-, 6-chloro-, 5,6-dichloro-, 2,6-dichloro- and 2,5,6-trichloro-3-trichloromethyl pyridine and 2,3,6-trichloro- and 2,3,5,6-tetrachloro pyridine. Vapor phase processes for chlorination of beta-picoline or beta-picoline hydrochloride, all operating in the temperature range of from about 300°C to about 500°C, are known. Clark U.S. Patent No. 3,412,095 describes a vapor phase beta-picoline chlorination process yielding 3-monochloromethyl pyridine. Bowden et al in U.S. Patent No. 4,205,175 describes a vapor phase chlorination process which yields a mixture of 2-chloro- and 6-chloro-3-trichloromethyl pyridine. Utility of these intermediates to produce herbicidal composition is also described. Nishiyama et al in U.S. Patent 4,241,213 also describes a vapor phase chlorination process to yield mixtures rich in 6-chloro-3-trichloromethyl pyridine. This compound is particularly useful as an intermediate for herbicidal compositions. Nishiyama in U.S. Patent No. 4,184,041 describes the utility of 5,6-dichloro-3-trichloromethyl pyridine in the production of herbicidal compositions.

Summary of the Invention

It has been discovered that high yields of mixtures rich in chlorinated picolines/pyridines may be achieved by non-catalytically chlorinating beta-picoline or beta-picoline hydrocholoride in a diluent in the liquid phase at temperatures of at least about 190°C while maintaining strong agitation and a feed ratio of chlorine to beta-picoline of at least about 5:1 by weight while feeding the chlorine and beta-picoline or beta-picoline hydrochloride to the reaction mass in a primary reactor. The beta-picoline can be dissolved in carbon tetrachloride or fed full strength into the reactor. It is desirable to have a supply of carbon tetrachloride available for flushing the feed line in the event of a shutdown because stagnant beta-picoline would otherwise tend to degrade in the feed line. If beta-picoline hydrochloride is the desired feed form, it is fed directly through a sparger into the bottom of the primary reactor. After the beta-picoline or beta-picoline hydrochloride has been partially chlorinated in the primary reactor, the polychloro picoline is subjected to further chlorination in one or more reactors for such times and temperatures as appropriate to maximize the yield of the desired end product or products.

The percent of volatiles realized by liquid phase chlorination according to the present invention is dependent upon on the diluent composition, the extent of mixing of the reactants and diluent, the picoline feed rate to reaction mass volume, the weight ratio of chlorine-to-picoline being fed, and the chlorine partial pressure, which influences chlorine solubility. The composition of the diluent media in which the reaction proceeds is important in practice of this invention, to secure good yields of the desired volatile chlorinated beta-picolines. Its function in this invention is quite different from the initiator charge described in Taplin U.S. Patent No. 3,424,754, which deals with alpha-picoline liquid phase chlorination. In U.S. Patent No. 3,424,754, the initiator charge has the function of evolving HCl when contacted with chlorine at the reaction temperature in order to react with alpha-picoline to form picoline hydrochloride. In the present invention the diluent's function is to be reactively less competitive for the chlorine dissolved in it and to help remove the heat of reaction evolved by the chlorination of the beta-picoline. Examples of some compounds usable as diluents in practice of the present invention, in that they generate one mole or less of HCl per mole of compound when contacted with chlorine under the reaction conditions of the present invention, are: 3-chloro-, 5-chloro-,

6-chloro-, 5,6-dichloro-, 3,5-dichloro-, 3,6-dichloro-, 3,4,5-trichloro- and 3,5,6-trichloro-2-trichloromethyl pyridine, 2-chloro-, 6-chloro-, 2,6-dichloro-3-trichloromethγl pyridine, and 2,3,6-trichloro-, 2, 3,5,6-tetrachloro- and

2,3,4,5,6-pentachloro pyridine, and mixtures thereof. This list is not meant to be exhaustive of all possible diluent constituents but is illustrative of compounds useful for the purpose. The diluent may be the chlorinated pyridine/picoline products from a previous reaction which meet the above criteria and is high in volatiles content.

In practice of the present invention, an excess of chlorine is fed relative to that needed for the beta-picoline and beta-picoline hydrochloride chlorination, which excess provides additional agitation and hence better mixing, and also a higher chlorine partial pressure which increases the chlorine solubility in the reaction media. A chlorine to beta-picoline weight ratio of at least about 5:1 is needed. As the temperature increases in excess of 200°C, the weight ratio of chlorine to beta-picoline fed needs to be higher in order to achieve the high yields of the desired volatile chloro-picolines. This is necessary because chlorine reacts more rapidly with the beta-picoline or beta-picoline hydrochloride as the temperature increases and therefore the chlorine dissolved in the reaction medium must be more rapidly replaced. This is accomplished by increasing the rate of chlorine addition relative to the beta-picoline flow rate which increases the chlorine partial pressure and hence its mole fraction in the liquid reaction medium. Gas solubilities tend to decrease with rising temperature, but an increase in system pressure also increases the chlorine solubility. The beta-picoline or beta-picoline hydrochloride feed is to be controlled relative to the reaction volume so no more than about 10% by volume of light phase accumulates relative to the chlorinated picoline phase at temperatures in excess of about 190°C. Potential decomposition products can result above this temperature in the absence of cooling and excess chlorine. Since beta-picoline hydrochloride and the diluent are somewhat immiscible and of different densities, good mixing is necessary in order to achieve dispersion of chlorine and beta-picoline or beta-picoline hydrochloride into the diluent.

Controlling these variables results in the high yields of volatile polychlorinated beta-picolines in the liquid phase at temperatures in excess of 190°C. Care must be taken to ensure metallic impurities such as iron, copper, aluminum and other Lewis Acid type metals are excluded from the reaction mass, as they will cause different reactions in the chlorination that may not be desirable.

Brief Description of the Drawings

FIG. 1 is a schematic diagram of a reaction system for practicing the process of the present invention on a continuous batch basis.

Description of the Preferred Embodiments

Example 1 FIG. 1 schematically illustrates a continuous batch type reaction system for producing mixtures rich in polychlorinated pyridine/picolines according to the present invention. Primary reactor R1, secondary reactor R2, and absorber C-2 are suitably glass of cylindrical configuration, electrically heated and each about 1 liter in volume, and with an inside diameter of 4 inches and an inside height of 7 inches. Finishing reactors Rr3A and R-3B are glass, spherical, electrically heated and about 1 liter in volume. Water cooled scrubber column C1 is suitably of cylindrical design, 1 1/2 inches in diameter, containing as packing some 18 inches of 1/4 inch glass rings.

Scrubber column C1 includes a holding tank or reservoir T1 and the overhead vapor from column C1 is delivered through vent line 10 to disengaging tank T2 in which the carbon tetrachloride collects, with the chlorine and hydrogen chloride evolving from column Cl being delivered by vent line 12 and sparged into hydrochlorination tank T3. For startup, beta-picoline hydrochloride, suitably previously prepared conventionally, as by sparging anhydrous HCl into a pool of beta-picoline maintained between 80°C and 100°C until saturated with HCl, is charged to hydrochlorination tank T3 and beta-picoline hydrochloride is withdrawn from tank T3 and delivered to bottom discharging sparger 14 in reactor Rl through line 16. An alternate startup mode involves feeding beta-picoline dissolved in carbon tetrachloride through lines 68 and 70 thence into line 14, generating hydrogen chloride which is vented to hydrochlorination tank T-3. For startup, also, primary reactor Rl was charged through charge line 18 with 1000 grams of diluent, consisting of chlorinated pyridine from a previous reaction (suitably comprising about 22.4% 6-chloro-, 48.9% 5,6-dichloro-, 27.3% 3,6-dichloro-, and 4.1% 4,6-dichloro-2-trichloromethyl pyridine by weight). 406 grams of like diluent material was also charged to secondary reactor R2 through charge line 20. 453 grams of a suitable absorbent was charged through charge line 64 to absorber C-2, the composition of the absorbent selected for this example being 66.7% 6-chloro-, 15.2% 5 , 6-dichloro-, 1.8% 3,6-dichloro-2-trichloromethyl pyridine and 4.9% 2,6-dichloro-, 4.9% 2, 3,5,6-tetrachloro- and 1.1%

2, 3,4,5, 6-pentachloropyridine, and 2.7% 5,6-dichloro-, 1.8% 2,6-dichloro-3-trichloromethyl pyridine, by weight. The absorbent charged to C-2 needs to have a melting point of less than 80°C and substantial solubility with carbon tetrachloride. Its purpose is to absorb higher melting chlorinated pyridines, e.g. those with melting points greater than 90°C, namely, 2, 3,5,6-tetra- and 2, 3, 4,5, 6-pentachloro pyridine. If these higher melting point chloropyridines were allowed to enter the scrubber column C-1 iri substantial quantity, they would tend to plug the column packing. The refluxing carbon tetrachloride in scrubber column C-1 tends to concentrate in the entrained chloropyridines that enter it in the bottom tank Tl thereof, and keep the overhead vapors substantially free of chlorinated pyridines which would otherwise plug the vapor outlet 10. Some typical examples which meet the criteria of suitable absorbent materials are 6-chloro-, 5 , 6-dichloro-, 3, 6-dichloro-, 3,5-dichloro-2-trichloromethyl pyridine, and mixtures thereof.

The operational startup sequence is that of introducing the diluent to the primary and secondary reactors, then initiating chlorine flow, then heating the reactors to desired reaction temperature, then initiating the beta-picoline or beta-picoline hydrochloride flow. By this procedure the beta-picoline or beta-picoline hydrochloride only sees excess chlorine in the reactors and degradation thereof to nonvolatiles is avoided. Once reactors R1 and R2 were charged, external heat was applied and the temperature of primary reactor R-1 thereof was maintained at 230°C, with secondary reactor R-2 being maintained at 150°C. and absorber C-2 maintained at 140°C. Chlorine gas from a suitable pressurized source was delivered to the reactor R1 through feed line 24 and bottom placed sparger 24 at a flow rate of 440 grams per hour. The flow rate of beta-picoline hydrochloride sparged into reactor Rl through bottom placed sparger 14, the discharge stream of which is closely adjacent (with about 1/2 inch spacing) to the discharge stream of chlorine sparger 24, was maintained at a rate equivalent to 29 grams beta-picoline per hour, amounting to a chlorine to picoline feed ratio of about 15:1.

As will be understood, the beta-picoline hydrochloride fed to primary reactor R1 releases hydrogen chloride from both the reaction with the chlorine and the decomposition of the hydrochloride salt. This hydrogen chloride along with excess chlorine is vented from reactor R1 through vent line 26 and sparged into the charge in secondary reactor R2 through bottom discharging sparger 28, the overhead vapor including hydrogen chloride and excess chlorine being vented from reactor R2 and delivered through line 30 to absorber C-2, thence through line 62 to scrubbing column C-1, thence through line 10 and line 12 to hydrochlorinating tank T3, the vapor flow from which passes through line 32 to hydrogen chloride and chlorine gas recovery means known per se, for recycling of the chlorine gas to the process and recovery of the hydrogen chloride, as desired. Once hydrogen chloride gas is being generated and is passing through the system to hydrochlorination tank T3, the beta-picoline feed into tank T3 through line 15 can be started if that is the desired feed mode.

Secondary reactor R2 is only partially charged with diluent at startup. This is for the reason that, as the volume of the reaction mass in reactor R1 increases in the course of the reaction, a portion of the reaction mass is moved from reactor R1 to reactor R2 (by volatilization and entrainment) through line 26 and through discharge line 34 for further chlorination in reactor R2. The temperature in secondary reactor R-2 influences the degree of continued chlorination. In this example the relatively low temperature of 150°C serves to quench the reaction occurring in primary reactor R-1 and to slow the rate of chlorination. A higher temperature in secondary reactor R-3, such as a temperature greater than 200°C, would continue the chlorination process at a higher rate than occurs at 150°C. In this example, reactors R-3A and 3B were chosen to take the reaction to the desired degree of chlorination by operating at 210°C for 12 hours.

When the liquid volume in secondary reactor R2 increases to the point where the reactor R2 is filled to its operating level, further increase in liquid volume is taken care of by progressively discharging the excess through line 36 to either finishing reactor R3A through line 38, or to finishing reactor R3B through line 40, depending on the setting of valve 42.

Chlorination to process end point is completed in either reactor R3A or reactor R3B by continued introduction of chlorine gas through bottom discharging sparger 44 or 46, with continued heating of the reactors R3A or R3B to a desired temperature for a desired time to yield the desired product distribution, e.g. a temperature of 210°C and a time of twelve hours, in this selected example. Chlorine and hydrochloride vapor takeoff from reactors R3A and R3B is delivered through vent lines 48, 50 to absorber C-2 through sparge line 74, thence to scrubber column C1.

Chlorinated reaction product is withdrawn from the reactors R3A and R3B through respective discharge lines 52, 54, with the product going to product purification means known per se, such as a vacuum fractional distillation column. Liquid discharge from holding tank T2 is delivered to scrubber column C1 through line 56 to return carbon tetrachloride to the column C1, with makeup of carbon tetrachloride from an appropriate supply if necessary, as indicated at 58. The liquid phase fraction collecting in bottom tank T1 of the scrubber column C1 is returned to absorber C-2, as indicated at line 60. Finishing reactors R3A and R3B can be smaller or larger than reactors R1 and R2, depending on the desired residence time to complete the chlorination reaction. For example, with a reaction temperature of 230°C. and a residence time of 12 hours in the primary reactor R1 and a reactor temperature of 150°C and a residence time of 12 hours in the secondary reactor R-2, the time required to complete the reaction in reactor R3A or in reactor R3B is about 12 hours at 210°C temperature. The controlling factor determining reaction time in reactor R3A or reactor R3B is the maximum concentration of the desired product. If the principal desired product is 5,6 dichloro-3-trichloromethyl pyridine, additional chlorination in R3A or R3B would be required for maximum recovery. If the principal desired product is 6-chloro-3-trichloromethyl pyridine, less time would be required in R3A or R3B. Correspondingly, additional time would be required to maximize the concentration of 2,3,6-trichloropyridine in R3A or R3B. In this first example it has been assumed that a mixture of end product compounds, with each compound present in substantial proportion, was desired, and to this end the composition of the end product obtained in R3A and R3B comprised 11.7% 2,3,6-trichloro pyridine, 24.4% 6-chloro-3-trichloromethyl pyridine, and 16.1% 5,6-dichloro-3-trichloromethyl pyridine, by weight.

Further, product purification and recycle to R3A or R3B for further chlorination, as indicated at 76, can convert the 5-chloro-3-trichloromethyl pyridine to 5,6-dichloro-3-trichloromethyl pyridine and 2-chloro- and 2,6-dichloro-3-trichloromethyl pyridine to 2,3,5-trichloro pyridine.

Excess chlorine, hydrogen chloride and some volatile corrosive chloro-picoline hydrochlorides and entrained chlorinated pyridines, some of which have melting points in excess of 100°C, are transferred to secondary reactor R2 from primary reactor R1 by heated vent line 26 and bottom discharging sparger 28, with the volatile hydrochlorides being absorbed and reacted further in secondary reactor R2. These hydrochlorides are very corrosive and tend to form solids on condenser surfaces that are in the 30°C to 100°C temperature range, the operating temperature range of scrubber column C1 and, along with the high melting chloropyridines, would there cause a plugging problem in column C1 if passed directly from primary reactor R1 to the scrubber column C1. Their absorption and further reaction in secondary reactor R2 help eliminate such plugging problems and absorber C-2 completely eliminates the high melting chloropyridines in the vent line 62 to column C-1. The excess chlorine, hydrogen chloride and entrained products passing to column C1 through absorber C-2 vent line 62 are there scrubbed with carbon tetrachloride discharged to column C1 through line 56. The entrained chlorinated pyridine products buildup in tank T1 and the liquid level therein is controlled by recycling the excess liquid back to absorber C-2 through discharge line 60. When the level in absorber C-2 reaches the operating level, processing of the excess material is begun through line 66 for removal of the high melting chloropyridine reaction products from the absorber material. These chlorinated pyridine products are removed from the absorbent material by vacuum distillation. Process absorbent is then recycled back to C-2 through line 64.

As will be apparent, finishing reactors R3A and R3B are operated in a batch manner, permitting one to be on line while the other is having the chlorinated product removed or is being filled from secondary reactor R2. Analysis of the reaction mass in the on line reactor R3A or R3B for maximum concentration of the desired chloropyridine(s) indicates when the reaction is finished-. When this occurs the contents of the on line reactor R3A or R3B are pumped through the respective discharge lines 52 or 54 to the purification section of the system, conventional per se. The residence time in each reactor R1, R2 and R3A or R3B typically varies from about 5 to about 40 hours, and the total cycle time in the reactors is about 10 to 120 hours. From the previously described feed and reaction conditions set forth in Example 1, 75 grams per hour of product was obtained that contained about 14.1% 5-chloro-, 24.4% 6--chloro-, 6.3% 2-chloro-, 16.1% 5,6-dichloro-, and 9.8% 2,6-dichloro-3-trichloromethyl pyridine, by weight. In addition, 11.7% 2,3,6-trichloropyridine was present. The volatiles content of the reaction mass was greater than 96%. As known per se, 2,3,6-trichloro pyridine can be separated and processed further through ferric chloride catalyzed liquid phase chlorination to 2, 3,5,6-tetrachloro pyridine, such as described in U.S. Patent 4,256,894. In this example, also, the total residence time was about 21 hours. In practice of the invention appropriate variation in residence time is determinable on a predictable basis, taking into consideration the product composition desired, and the reactor pressure and reactor temperature. In addition, the quantity of diluent recycled to the reactors may also be varied to vary the residence time. In any event, as earlier indicated, the feed rate of beta-picoline or beta-picoline hydrochloride relative to the reaction volume is to be controlled so that no greater than about 10% by volume of lighter phase (undiluted picoline hydrochloride) exists in the reaction mass.

The gases in vent line 32 from hydrochlorination tank T3 are predominantly excess chlorine and hydrogen chloride, which stream can be separated or purified by a number of conventional techniques such as absorption of the hydrogen chloride in water, or drying the chlorine and compressing the chlorine gas for recycle, or fractional distillation. EXAMPLE 2

Utilizing the same reaction system shown in FIG. 1 and described in Example 1, reactors Rl and R2 were respectively charged with 928 grams and 635 grams of chlorinated picoline diluent from a previous reaction. Absorber C-2 was charged with 585 grams of the same material. The composition of the diluent was 4% pentachloropyridine, 54% 6-chloro-, 15% 6-dichloro-, and 2% 4,6-dichloro-2-trichloromethyl pyridine, and 6.3% 6-chloro-, 2% 2-chloro-, 1.5% 5,6-dichloro- and 1.5% 2,6-dichloro-3-trichloromethyl pyridine, by weight.

Chlorine at a flow rate of 440 grams per hour was sparged into reactor Rl and reactors Rl and R2 were heated to temperatures of 210°C and 150°C respectively. Absorber C-2 was maintained at 140°C. Beta-picoline was then sparged into reactor R1 through sparger 26 after being premixed with about an equal volume of carbon tetrachloride. The beta-picoline feed was at a rate equivalent to about 20 grams beta-picoline per hour. The average residence time of the reaction mass in each of the reactors R1 and R2 was about 12 hours. Chlorination of the effluent from reactor R2 was continued in reactor R3A for 9 hours at 160°C and then for 5 hours at 190°C. The resulting reaction product contained about 21% 5,6-dichloro-3-trichloromethyl pyridine by weight, and the volatile content of the reaction mass was greater than 98%.

The analyses of the reaction products obtained in Examples 1 and 2 are given in the following Table ONE.

EXAMPLES 3 through 7 Examples 3 through 7 serve to illustrate some of the process variables which can occur in practice of the present invention, and for such purpose were conducted as simplified batch processes. A chlorination reactor comprising a 1000 ml spherical glass reactor, heated by an electric heating mantle, was equipped with two sparge tubes and a line which was vented through a 5000 ml glass knockout pot to a caustic scrubber. The spargers were bottom placed and closely spaced (2 centimeters apart) and the respective feed lines to the spargers were fed through rotometers and flow controlled through respective needle valves, one being supplied from the source of chlorine gas, and the other supplied from a source of beta-picoline (Examples 3 and 4) or beta-picoline hydrochloride (Examples 5-7). In each run the procedure followed was the same except for the variables investigated, namely diluent composition, temperature, chlorine-to-picoline feed ratio, residence time, and picoline flow rate relative to reaction mass volume. In Example 3, which is illustrative, the reactor was charged with 715 grams of diluent, the composition of which is given in the following TABLE TWO, and chlorine feed was initiated through the chlorine sparger at the rate of 380 grams per hour and the charge heated to a temperature of 235°C. Beta-picoline dissolved in an equal volume of carbon tetrachloride was then sparged into the reactor at the rate of about 28 grams per hour for a period of 5 hours. The weight ratio of chlorine to the beta-picoline being fed during the reaction was about 13.5:1. Chlorine feed was continued at the rate of 380 grams per hour for 9 more hours at a temperature of 210°C after the picoline feed was discontinued. The reaction process parameters are tabulated in the following TABLE THREE. The gross weight of the resulting reaction product was 1065 grams, indicating a net production of 350 grams of product. The product was a clear tractable fluid, with a volatiles proportion of greater than 98%, as measured by internal standard gas chromatography. The constituency of the product was as tabulated in TABLE THREE. As indicated, additional runs, designated Examples 4, 5, 6 and 7 involved the diluents set forth in TABLE TWO, the parameters set forth in TABLE THREE and produced reaction products comprising the compounds set forth in TABLE FOUR.

An important aspect of the present invention is the discovery that further liquid phase chlorination of certain monochloro and dichloro-3-trichloromethyl pyridines, in liquid phase and at a temperature of at least about 190°C, can be effected in a chlorinating reactor, such as finishing reactors R3A and R3B, to realize valuable dichloro- and trichloro-3-trichloromethyl pyridines and trichloro and tetrachloro pyridines. As will be apparent, this aspect of the invention is applicable to effluent mixtures from reactor R2 in the foregoing examples, and also to monochloro and dichloro-3-trichloromethyl pyridines and mixtures thereof prepared by other processes, such as the chlorinated beta-piσolines produced by the vapor phase processes disclosed in Bowden et al U.S. Patent 4,205,175 ( 2-chloro- and 6-chloro-3-trichloromethyl pyridine), as well as Nishiyama U.S. Patent 4,241,213 (6-chloro-3-trichloromethyl pyridine). The following Examples 8 through 12 are presented to illustrate chlorination products obtained by continued liquid phase chlorination of mixtures rich in monochloro and dichloro-3-trichloromethyl pyridines, such as those obtained in the effluent mixtures from reactor R2 by the process of the present invention, or which may be otherwise obtained or available from other chlorination processes.

EXAMPLE 8

In Example 8 shown in TABLE FIVE, 100 grams of a mixture rich in 6-chloro- and 2-chloro-3-trichloromethyl pyridine were chlorinated in the liquid phase at 190°C. After two hours the reactor was sampled and a significant decrease in the concentrations of the 6-chloro- and 2-chloro-3-trichloromethyl pyridine was noted, i.e. 15.6% decreased to 9.6% and 7.8% decreased to 2.8% respectively. A corresponding increase in the concentration of 2,6-dichloro-3-trichloromethyl pyridine was noted, i.e. 5.3% to 13.0%. The following reactions were therefore occurring at this stage of process:

Example 9 illustrates an additional chlorination reaction occurring in this liquid phase system, namely

One hundred grams of a mixture rich in 6-chloro- and

2,6-dichloro-3-trichloromethyl pyridine was chlorinated for 4 hours in the liquid phase at 210°C. The 6-chloro-3-trichloromethyl pyridine concentration decreased from 6.9% to 2.1% during this time, while the 2,6-dichloro-3-trichloromethyl pyridine concentration increased only slightly from 12.9% to 14.3%. Concentration of 2,3,6-trichloropyridine increased from 2.3% to 6.3%.

EXAMPLE 10

Liquid chlorination of a mixture rich in

2,3,6-trichloropyridine catalyzed with four weight percent ferric chloride is illustrated in TABLE SEVEN and Example 10. Fifty grams of a mixture rich in 2, 3,6-trichloropyridine was chlorinated at 195°C for 4 1/4 hours. The concentration of 2,3,6-trichloropyridine decreased from 89.4% to 1.7% while the concentration of 2,3,5,6 tetrachloropyridine increased from 4.5% to 97.6%.

It has been demonstrated that various liquid phase, uncatalyzed and catalyzed chlorinations result in a method of producing mixtures rich in

2, 3 ,5 ,6-tetrachloropyridine, if desired. Useful chlorinated pyridines such as 6-σhloro-3-trichloromethyl pyridine may be separated out by vacuum distillation prior to their chlorination, if desired. EXAMPLE 11 This example illustrates the conversion of 5-chloro-3-trichloromethyl to

5,6-dichloro-3-trichloromethyl pyridine by liquid phase chlorination.

One hundred grams of a mixture rich in 5-chloro- and 5,6-dichloro-3-trichloromethyl pyridine was chlorinated in the liquid phase to a mixture richer in 5,6-dichloro-3-trichloromethyl pyridine and in 2,5,6-trichloro-3-trichloromethyl pyridine. TABLE EIGHT illustrates the results.

Example 12 970 grams of products rich in 5,6 dichloro- and 2,5,6-trichloro-3-trichloromethyl pyridine were charged to a chlorinator. 200 grams per hour of chlorine was sparged into the bottom of the chlorinator for 8 hours at a reaction temperature of 260°C and for 3 hours at a reactor temperature of 230°C. The

5,6-dichloro-3-trichloromethyl pyridine content decreased from 10.6 mole percent to 4.3 mole percent, while 2,5,6-trichloro-3-trichloromethyl pyridine content decreased from 19.1 mole percent to 9.2 mole percent. The 2,3,5,6-tetrachloro pyridine content of the mass increased from 28.5 mole percent to 44.2 mole percent. In summary:

The above reactions occur during the production of 2, 3,5,6-tetrachloro pyridine from 5,6-dichloro-3-trichloromethyl pyridine via 2,5,6-trichloro-3-trichloromethyl pyridine.

In composite, the foregoing Examples 8 through 10 demonstrate that liquid phase chlorination carried out in a diluent and at a temperature of at least about 190°C while sparging chlorine into a reactor charge progressively converts 2-chloro-3-trichloromethyl pyridine and/or 6-chloro-3-trichloromethyl pyridine to 2,6-dichloro-3-trichloromethyl pyridine, which then converts to 2,3,6-trichloro pyridine and then in turn to 2,3,5,6-tetrachloro pyridine. Such conversion may be selectively controlled to be on a substantially quantitative basis, or can produce some intermediate mixture, depending on the time the chlorination is maintained. Similarly, Examples 11 and 12 demonstrate that chlorination under like conditions of mixtures rich in 5-chloro-3-trichloromethyl pyridine and 5,6-dichloro-3-trichloromethyl pyridine forms mixtures richer in 5,6-dichloro-3-trichloromethyl pyridine, along with further conversion thereof to

2,5,6-trichloro-3-trichloromethyl pyridine, the 2,5,6-trichloro-3-trichloromethyl pyridine being converted in turn to 2,3,5,6-tetrachloro pyridine. Such extent of conversion of these monochloro and dichloro-3-trichloromethyl pyridines to the indicated dichloro- and trichloro-3-trichloromethyl pyridines and the indicated trichloro and tetrachloro pyridines by direct chlorination is considered unique and provides valuable intermediates for subsequent manufacture of herbicides and insecticides by a much simpler and more straightforward process than heretofore known. The reaction mechanism involved in the liquid phase chlorination of beta-picoline appears to be such that at temperatures less than about 190°C in the primary reactor 2,4,6-trichloro-3-trichloromethyl pyridine is formed, by a progression from the monochloro trichloromethyl to the dichloro trichloromethyl and then to the trichloromethyl, with the final product being 2,4,6-chloro-3-trichloromethyl pyridine, for which there is no known utility. Yield averages in the temperature range from 100°C to about 180°C prove to be from 60% to 70%, so reaction products at primary reactor temperatures less than 190°C do not appear to have much utility. We have now discovered, however, that at primary reactor temperatures from 190°C up to higher liquid phase chlorination temperatures, e.g. 250°C, a whole series of useful reaction products is realized, and at temperatures about 220°C and above there is very little 2,4,6-trichloro-3-trichloromethyl pyridine formed. Typical product compositions at 220°C and higher reaction temperatures in the primary reactor involve about 10% 5-chloro-3-trichloromethyl pyridine, 40% 6-chloro-3-trichloromethyl pyridine, 20% 2-chloro-3-trichloromelthyl pyridine by weight and smaller amounts on the order of 1 to 2% of the 5,6-dichloro-3-trichloromethyl pyridine and the 2,6-dichloro-3-trichloromethyl pyridine. As earlier indicated, we have also discovered that these products can be further chlorinated, at predictible functions of time vs. temperature, to give other useful intermediates. For example, when subjected to further chlorination in liquid phase at high temperature, 5-chloro-3-trichloromethyl pyridine goes to 5,6-dichloro-3-trichloromethyl pyridine. Similarly 6-chloro-3-trichloromethyl pyridine chlorinates to the 2,6-dichloro-3-trichloromethyl pyridine as does the 2-chloro-3-trichloromethyl pyridine. The process can be interrupted at this stage and these two main components, namely the 5,6-dichloro-3-trichloromethyl pyridine and the 2,6-dichloro-3-trichloromethyl pyridine may be separated out, or, if chlorination is continued, the 5,6-dichloro-3-trichloromethyl pyridine goes to 2,5,6-trichloro-3-trichloromethyl pyridine and on still further chlorination to 2,3,5,6-tetrachloro pyridine, which has great utility as an intermediate in insecticidal compositions. The 2,6-dichloro-3-trichloromethyl pyridine can be chlorinated further to 2,3,6-trichloro pyridine. The 2,3,6-trichloro pyridine also can be chlorinated with ferric chloride catalyst to 2,3,5,6-tetrachloro pyridine. The process can be selectively controlled to realize a very high yield of 2,3,5,6-tetrachloro pyridine, or the yield of 5,6-dichloro-3-trichloromethyl pyridine and 6-chloro-3-trichloromethyl pyridine, both of which have utility as intermediates for herbicides, can be maximized by not chlorinating as long.

In general, the primary reactor R1 is maintained at a temperature of at least 190°. Its maximum practical temperature for practice of the present invention is that temperature at which it can be safely operated in the liquid phase. Retention time in the primary reactor R1 should also be such that there is no unreacted beta picoline or beta picoline hydrochloride in vent line 26 or in the liquid passed to the secondary reactor R2 through line 34. In what is considered the best mode for practice of the invention (Example 1), the secondary reactor R2 is maintined at 150°C. This relatively low temperature in reactor R2 serves two purposes. It effectively slows the reaction down so further chlorinations are controlled and the desired end point is not overshot. In addition, the lower temperature in R2 helps to absorb and quench the very hot overhead vapor from reactor R1 and makes it easier for absorber C2 to be maintained at its relatively low operating temperature (140°C), so that it will effectively of keep the high melting point pyridines from being carried over into scrubbing column C1 and plugging it up. Secondary reactor R2, when operated at a temperature substantially lower than the primary reactor R1, serves as what might be termed a buffering or stabilizer reactor. It need not be cooler than reactor R1, however. It all depends on what end products are desired. Finishing reactors R3A and R3B are also run at a selected temperature, 210°C in the case of Example 1, and a selected time, 12 hours in Example 1, to get a maximum composition of the desired products, e.g. in Example 1 to get 6-chloro- and 5,6-dichloro-3-trichloromethyl pyridine and the derivatives that go to 2,3,6-trichloro pyridines on further chlorination. If the reaction objective is to make a product rich in 2, 3,6-trichloro pyridine and

2,3,5,6-trichloro pyridine, secondary reactor R2 should be run very hot and the finishing reactors R3A and R3B also should be run very hot for a very long period of time, since these final products are "at the end of the line", from the point of view of progressive chlorination reaction.

The main criteria for the absorbent charge in absorber C2 is that it is nonreactive at the temperature at which the absorber operates (140°C), is a compound or mixture of compounds having a melting point less than 80°C, and is mutually soluble in carbon tetrachloride so that it doesn't plug up the scrubbing column C1, either through melting or freezing or lack of solubilization. The absorber charge, being nonreactive, is basically is a one time charge and recycled after removal of the absorbed product components, with only slight makeup from time to time. Functionally, the absorbent acts and is handled in much the same way as the carbon tetrachloride in the scrubbing column C1. The chlorination process described in Taplin U.S. Patent 3,424,754 relies on chlorine gas sparging into the liquid reaction mass to dissolve the chlorine in the reaction mass and to mix alpha-picoline hydrochloride with the initiator charge. According to Chemical Engineering Handbook, Perry, 3d Edition, page 1215 (1950), agitation produced by the degree of gas sparging involved in the process of U.S. Patent 3,424,754 (estimated to be about 1.5 cubic foot per square foot minute at 200°C) is usually too mild to move immiscible liquids with appreciable density differences into good contact with each other. In reactions according to the present invention, it is a practical necessity to maintain the reaction mass well mixed so that there is good contact and quick dispersion of the beta-picoline hydrochloride into the diluent at the desired reaction temperatures of greater than 190°C because the polychlorinated pyridine diluent and the beta-picoline hydrochloride are immiscible and have substantially different densities (about 1.6 and about 1.2 grams per cubic centimeter, respectively), and because beta-picoline hydrochloride is unstable in this temperature range, i.e. the salt tends to break down to its components, namely hydrogen chloride and beta-picoline. If there is breakdown into the components, the hydrogen chloride is volatile and escapes through the vent system and beta-picoline builds up in a lighter liquid phase. Experimentation has shown that chlorinating beta-picoline hydrochloride in the absence of a diluent at a temperature in excess of 160°C results in intractable mixtures of tars and polymers. Such tendency to form higher molecular weight reaction products increases at higher reaction temperatures.

Yields of volatile chlorinated picolines in excess of 99% and other new useful products are obtained when care is taken to ensure a high partial pressure of chlorine and sufficient mixing and quick dispersion of the beta-picoline or beta-picoline hydrochloride into a chlorine rich diluent which does not substantially compete for the available chlorine. This is accomplished by sparging chlorine (in excess of that needed for the reaction) and beta-picoline or beta-picoline hydrochloride at closely spaced locations near the bottom of the reactor means containing the polychlorinated pyridine diluent charge. The mixing required to ensure adequate contact between the liquids and gas can be achieved by high gas flow rate sparging, mechanical agitation, or a combination of both. High gas flow rates as described by Braulich, A.J.; Ch. E. Journal, Volume 11, No. 1, pp 73-79, can achieve mixing of a magnitude almost equivalent to high power input mechanical mixing. Several disadvantages are inherent in the use of high gas flow rates, however. They are:

(a) high entrainment of the reactor liquids to the scrubber column C1 where they are scrubbed with carbon tetrachloride and must be recycled to the reaction system.

(b) a large volume of chlorine gas which must be purified, dried, and recycled.

Another mode of operation to enhance mixing is to combine mechanical agitation with chlorine gas and beta-picoline or beta-picoline hydrochloride sparging to achieve the desired degree of mixing and excess chlorine. High maintenance of mechanical seals and agitators are some of the disadvantages of such a mechanical agitation system.

An increase in reactor back pressure aids in increasing the chlorine concentration in the reaction liquid. The stoichiometric amount of chlorine reacted per pound of beta-picoline fed is greater than 3:1 by weight. Chlorine in excess of the stiochiometric requirement is considered essential to ensure that the beta-picoline or beta-picoline hydrochloride does not form undesirable tars and polymers. Therefore, weight ratios of at least about 5:1 of chlorine to beta-picoline being fed are deemed necessary in practice of the present process.

Care must be taken not to exceed the thermal stability of the diluent system. Diluents such as 6-σhloro- or 5,6-dichloro-2-trichloromethyl pyridine can decompose vigorously at temperatures greater than 260°C.