US2694070A

US2694070A - Process for preparing pyridine carboxylic acids

Info

Publication number: US2694070A
Application number: US278746A
Authority: US
Inventors: Andrew J Martin
Original assignee: Allied Chemical and Dye Corp
Current assignee: Allied Corp
Priority date: 1952-03-26
Filing date: 1952-03-26
Publication date: 1954-11-09
Anticipated expiration: 1971-11-09

Description

United States Patent fitice 2,694,070 Patented Nov. 9, 1954 PROCESS FOR PREPARING PYRIDINE CARBOXYLIC ACIDS No Drawing. Application March 26, 1952,

.Serial No. 278,746

11 Claims. (Cl. 260-2955) This invention relates to a process for the oxidation to pyridine carboxylic acids of heterocyclic aromatic nitrogen compounds containing a single pyridine nucleus and having at least one oxidizable hydrocarbon group, attached to the pyridine nucleus by at least one carbonto-carbon linkage, and more particularly to the production of nicotinic acid from certain compounds of this type.

Pyridine carboxylic acids are useful as intermediates in various organic reactions and in the pharmaceutical field. Of these acids, 3-pyridine carboxylic acid, i. e. nicotinic acid (Niacin) is a member of the vitamin B complex group and is useful in the enrichment of foods to improve their nutritional values.

Substituted pyridine and quinoline type compounds of the character described have been oxidized in the past to pyridine carboxylic acids by a number of methods including oxidation with sulfuric acid at high temperatures in the presence of a catalyst. Such oxidations, using sulfuric acid as the sole oxidizing agent, are usually carried out at temperatures between about 305 C. and about 325 C. and even at these temperatures and with catalytic acid require considerable time for completion of the oxidation reaction, usually fromabout 6 to about 24 hours in the presence of a selenium catalyst.

Efforts to provide processes which could be carried out at lower temperatures and/ or in shorter times, have resulted in the use, for example, of nitric acid or perchloric acid as oxidizing agents in sulfuric acid medium with or without catalysts. These processes, while satisfactory from the point of view of rapidity and lower temperature operation, nevertheless, require the use and handling of liquid oxidizing agents which are expensive and which from time to time are in short supply.

I have now found that pyridine carboxylic acids may be prepared rapidly, in good yields, at low temperatures, without resort to auxiliary liquid oxidizing agents, ac-

. cording to my invention wherein l etcrocyclic nitrogen compounds containing a single pyridine nucleus and hav-' ing at least one oxidizable hydrocarbon group attached to the pyridine nucleus by at least one carbon-to-carbon linkage are oxidized in the liquid phase to pyridine carboxylic acids by concentrated sulfuric acid aided by gaseous nitrosyl chloride as an auxiliary oxidizing agent.

As examples of such compounds susceptible to oxidation by the process of the present invention there may be mentioned quinoline, isoquinoline, the picolines or methyl pyridines, such as 2-picoline, 3-picoline and 4- picoline, the lutidines or dimethyl pyridines, the collidines, for example y-collidine or trimethyl pyridine and aldehyde collidine or Z-methyl-S-ethyl pyridine, as well as the methyl quinolines, methyl isoquinolines, 5- and 8- nitroquinolines, 5- and 8-hydroxy quinolines, etc.

If the heterocyclic aromatic nitrogen compound of the character described has an oxidizable hydrocarbon substituent attached to the tion only, has no unoxidizable substituent group on the pyridine nucleus and has not more than two additional oxidizable substituents on the pyridine nucleus each of which is in an alpha position, its oxidation will produce nicotinic acid, either directly in the case of compounds having a single beta substituent such as 3-picoline, or indirectly in the case of poly substituted compounds by oxidation of all the substituents followed by decarboxylation of all but a single beta carboxylic acid group.

I have found that gaseous nitrosyl chloride (NOCl) which is an inexpensive waste material available in large pyridine nucleus in one beta posi 2 quantities as a by-product of chlorine manufacture, when introduced into a sulfuric acid solution of a heterocyclic nitrogen compound of the character described, at oxida tion temperatures, either in the absence of a catalyst or in the presence of a catalyst such as a selenium-contain ing catalyst, acts as an auxiliary oxidizing agent, mark edly to accelerate the rate of the sulfuric acid oxidation. Under certain conditions its action is that of a supplementary oxidizing agent which term, when used herein, means that when such agent is used in conjunction with sulfuric acid in the oxidation of a heterocyclic nitrogen compound, there results a higher rate of oxidation than is obtained by the use of sulfuric acid alone under otherwise identical conditions, but a rate not higher than the additive oxidation rate attributable to both sulfuric acid and the auxiliary oxidizing agent combined. Under certain other conditions the nitrosyl chloride acts as a promoter, which term, when used herein, means that the auxiliary oxidizing agent, when used in conjunction with sulfuric acid in the oxidation of a heterocyclic nitrogen compouud, results in a higher rate of oxidation than the additive oxidation rate attributable to both sulfuric acid and the added oxidizing agent combined. The term auxiliary oxidizing agent is used herein as a generic term to denote both supplementary oxidizing agents and promoters; and auxiliary oxidizing action is used to denote the production of any increase, however small or large, in the oxidation rate over that produced by sulfuric acid alone and includes both supplementary oxidizing action and promoter action.

An auxiliary oxidizing effect on the sulfuric acid oxidation of heterocyclic nitrogen compounds is exerted by nitrosyl chloride ineither the presence or the absence of a catalyst. Sulfuric acid alone, in the absence of a catalyst, produces virtually no conversion of heterocyclic nitrogen compounds to pyridine carboxylic acids, even when heated at elevated temperatures of the order of 300 C. for prolonged periods of 10 hours or more. With the aid of a selenium type catalyst, complete conversions to pyridine carboxylic acids by sulfuric acid alone require periods ranging between about 6 and about 24 hours. Using nitrosyl chloride as an auxiliary oxidizing agent accordlng to the process of my invention and carrylngout the oxidation at temperatures between about 240 C. and about 300 C., complete conversions may be obtained in the presence of a catalyst such as a selenium catalyst, in periods varying between about 30 minutes and about 2 hours depending on the temperature and rate of nitrosyl chloride input and the particular heterocyclic nitrogen compound oxidized.-

In carrying out the process according to my invention, the heterocyclic aromatic nitrogen base compound, dissolved in concentrated sulfuric acid, is subjected to the action of nitrosyl chloride at elevated temperatures in e presence or absence of a catalyst. In a preferred method of carrying out the process, the heterocyclic aromatic nitrogen base compound is mixed with sufficient concentrated sulfuric acid to provide at least-a slight excess thereof over that required to form the nitrogen base sulfate and to maintain such an excess during the A catalyst such as selenium or a selenium compound is added to the charge and, after bringing the charge to oxidizing temperature, the gaseous :NOCl auxiliary oxidizing agent is passed into the hot solution. Flow rate of NOCl may be controlled to provide the optimum or desired supplementary or promoter oxidizing action at the particular oxidizing temperature and the oxidation is continued until the desired conversion of heterocyclic nitrogen compound is attained.

Quantities of catalyst, such as selenium or selenium compound catalyst, used may be between about .5% and about 25% based on the weight of the heterocyclic nitrogen compound used. The sulfuric acid used is concentrated sulfuric acid, i. e. from about to the ordinary concentrated sulfuric acid of commerce (95-96%) being satisfactory.

The temperatures at which the oxidation of the hetero- .cyclic nitrogen compounds described may be carried out using the gaseous nitrosyl chloride auxiliary oxidizing agent according to my invention, are somewhat lower than the optimum temperatures required for oxidation of the same heterocyclic nitrogen compound with sulfuric acid alone. Thus, whereas the optimum temperature for oxidizing quinoline to nicotinic acid by means of H280; in the presence of a selenium catalyst lies between about 295 C. and about 315 C. and for oxidizing S-picoline lies between about 305 C. and about 315 C., the optimum oxidation temperature when using nitrosyl chloride in its auxiliary oxidizing capacity lies in the neighborhood of 270 C. Suitable temperature ranges within which supplemental oxidizing action is exerted by nitrosyl chloride are between about 240 C. and about 300 C. At 270 Ci about C. the nitrosyl chloride exerts at least a supplementary oxidizing action in the case of all the heterocyclic nitrogen compounds as defined, and, in the case of poly substituted pyridine ring compounds such as quinoline, isoquinoline and Z-methyl-S-ethyl pyridine it exerts a promoter action as well.

The rate at which nitrosyl chloride may be introduced into the charge may vary. For maximtun oxidation hastening efr'ect however, it preferably should be introduced as rapidly as it will be completely absorbed, but slowly enough so that little if any passes out of the charge. This rate varies markedly with the stage of the reaction, larger relative proportions of nitrosyl chloride being generally utilizable in the early stages of the oxidation than near its completion. In general, I find that introduction of nitrosyl chloride should be made at a rate of at least about 1 part by weight per minute per 100 parts of heterocyclic nitrogen compound, and may be as high as about parts per minute or higher, at least during the early stages of the oxidation; the rate may be decreased somewhat during the later stages if desired when and if nitrosyl chloride begins to appear in the exit gases. Usually a flow rate between about 2.5 parts and about 10 parts per minute is satisfactory. The total quantity used will vary somewhat depending on the particular heterocyclic nitrogen compound being oxidized, the temperature and the rate of introduction of NOCl, but in general should be sufiicient to insure production of the desired supplementary or promoter action under the conditions of the oxidation. This quantity will usually lie within the range between about 125 parts and about 650 parts per 100 parts by weight of the heterocyclic nitrogen compound.

The oxidation of representative heterocyclic nitrogen bases with sulfuric acid alone proceeds according to the equations set out below (Series A) for quinoline, the picolines and Z-methyl-S-ethyl pyridine respectively,

A. Theoretical oxidation of nitrogen bases with sulfuric acid The oxidation of the same representative heterocyclic nitrogen bases theoretically would proceed according to the equations set out below if all the oxidation were at-' tributable to nitrosyl chloride alone (Series B),

One of the outstanding advantages of the present invention in addition to its inexpensiveness, is the increased rate of oxidation of heterocyclic nitrogen compounds as described, to pyridine carboxylic acids over that possible with sulfuric acid alone within the temperature range defined. The amount of this rate increase depends to some extent on the temperature, to some extent appears to be inherent in the compounds oxidized.

The increase in reaction rate induced by nitrosyl chloride over the rate of reaction using sulfuric acid alone may readily be demonstrated and measured by comparing the results obtained by bubbling nitrosyl chloride through the sulfuric acid reaction mixture, with the results obtained by bubbling an inert gas such as nitrogen through an identical oxidation mixture at the same temperature. Any loss of weight incurred in the oxidation mixture through which nitrogen is passed, will be attributable to oxidation by sulfuric acid alone, the nitrogen having no chemical effect but reproducing the physical conditions of the nitrosyl chloride-treated material by furnishing similar agitation. The loss of weight is due to loss of CO2,SO2 and water vapor by volatilization as illustrated in the foregoing equations. The weight loss occurring in the oxidation mixture through which nitrosyl chloride is passed will be due to a combination of sulfuric acid oxidation and nitrosyl chloride oxidation. A comparison of weight losses at constant conversions and temperatures in the two types of oxidations gives a measure of the rate increase attributable to the nitrosyl chloride. Whether such rate increase represents merely a supplementary oxidizing effect as defined, or represents a promoter (synergistic) effect, may be ascertained by calculating the percent conversion theoretically ascribable to nitrosyl chloride on the basis of the equations set out above, adding this theoretical conversion to the conversion figure obtained using H2804 alone under comparable conditions, and comparing this total with the conversion actually obtained by the combined action of sulfuric acid and the auxiliary oxidizing agent. Positive diiferences are construed as evidence of promoter action; negative differences correspond to incomplete utilization of the auxiliary oxidizing agent. The degree of supplementary oxidizing effect may be ascertained by noting the improvement in percent conversion obtained when using the auxiliary oxidizing agent over the percent conversion obtained when using sulfuric acid alone under comparable conditions, all as brought out in the following specific examples which further illustrate my invention. In these examples, the figures shown for percent conversion are calculated from the total quantity of heterocyclic nitrogen base used up in the reaction, the resulting reaction product being essentially the acid indicated, together with small quantities of CO2 and ammoma.

EXAMPLE 1 I Quinoline was oxidized to nicotinic acid using sulfuric ac d as the primary oxidizing agent and nitrosyl chloride as auxiliary oxidizing agent at about 270 C.

@QQQMQ The p aratu used as a -seek; equipped with a as n t tube. th mometer. hermo ouple well and. ah: eeeds se he flask heated ya quartz hemisnheni a mantle and mper tu e controll d by: than mocouple connected entire apparatus (mantle and flask) was placed in a balance in a manner such that smallweight changes in the charge were readily detectable.

In c ryin ut h un, t flask wa h rged. with 2 parts of selenium as ca alyst and 5,16% solution of quinol'ine 95%. clgargg was brought rapidly to, op 05 s f utie acid; The. ratin tempenat re n 1,5 t m nht s; wh re itwasme ntains Nitrosyl chloride. at room, temperature, Qabout- 25. (1.). was then passed into the hot solution at a rate of, 0.5 liter (.02 mol) per minute or 1.3 parts by weight per minute. As the oxidation; progressed the weight of the charge decreased due to evolution of gaseous products tion o he: quino ii e. Weight. loss s were re: corded periodically: and at the same. time samplesxof the charge were analysed for conversion of the qu-inoiine to nicotinic acid and the results recorded.

Progress of) the, oxidation is shown in Table 1A below.

Table 1A Av run carried-out in a. manner: identical in all respects to the above except that nitrogen waspassedthrough' the charge inplace of nitrosyl chloride, gayethe results shown. in Table 1B: below.

Table 1B [Weight loss during oxidation oi quiHO1inB.,With,H2sQL at. 270.

' introduction 0 f N2 at 0 .'5 literper lnlnute],

gas. was, oneliter; per. minute (246 parts, by. weight; per weight minute) Wltli. the results, listed; m, Table. 3A below. Elapsed Time, Minutes Tabla} 3 53; Weight loss'andconversion ofquinoli'ne during oxidation with HtSOi 15v v at 270 0. supplemented by NQOltlntroduced at 1 liter per minute] 30 n v. 5. 60' v l Wright P t 120- .t e ercen 210- i Elap-sed-Tme"Mmutes -Izoss;Parts Conversion" in 5, i .l 5

In Table 1C below, the conversion of quinoline by 1?? I 5%? sulfuric acid alone, and that. theoretically ascribable to 1. nitrosyl chloride alone under comparable conditions as 6m to 14 a 39.15:, calculated from the-equatronsam; C(31l1mIl'S3.-al1d-i4; are.

listed and the totals of-thesetwo effects are-listedi The actual-conversion found is also listed together-with the improvement-in conversion oven-HzSOnalone andover the theoretical total of H2SO4- and i nitrqsyl; chloride.

Table 1C Conversion in'percentmi qulnoline during oxidation at-.:270 O. with,

HgSOl alqneand with-introductionof N001 at 0.5 lltepiaet minute] Total Improve- Improve-- Time, 5 8 9 5 338 H2SO Actual ment over ment over Min. Found No.01, Total; 1118.04. Theoreti- Theory f alone; calTotal.

l5 14 7. 5 21. 5 38. 5 31.0 +17 30 28. 5 15 43. 5 59. 3 44. 3 +15. 8 4s 22. 5;. 65. 5; 73.8 51. a +8.3 57 30 87 84. 0 54 -3. 0 71. 5 85.0

with 29. p r s of a 10 6 exAMPItE; 2.,

Another 0.1- quiholi'ne; to nicotinicacid was;

carried out in a manner identical with that employed in to a1pgqtgnfiomgtemcgnmoucn The! 5; Example 1 except that the: oxidation temperature was 2.4.0, C.,, with the. results. listed. in Table. 2A below...

Tizbl'e" 221 i Weight 1 Percent Elapsed Time Minutes Loss,,1 arts Conversion the conversion of quiholine: by that theoretically ascribabl'eto Il'n 'Fa-ble 28 below; sulfuric acid alone and 20: nitrosyl chloride under comparable conditions as calcul'ated tom the equations: in columns 3 and 4', are. listed;

and the totals of these two effects are listed. The actualconversion found is also listedtogether with improvements in conversion over H2504 alone and over the theoretical-r total? of: H2594. andi nitrosyl chloride.

Table. 2B

[ on ersion nt nercent: at quino line; d'urin 7 H1804 alone and with introduction of NO 1 at 0.5 liter per minute].

mi ditions of then'un NOCllexerts. asupplementary oxidizing- It will be, observed from Table 28' that under the con.-

action, although noobservable promoter action.-

EXAMPLE Another. oxidation of quinoline to nicotinic. acid. was, with. 45: carried. qutin. a. manner. identical. with that employed 1n .EXample 1..exceptthat the rate offintrodnction ofNoC'I.

Ina--runcarried-out in a manner identical in all re-- SQElJ-S? with: hat; described. above: except: that. nitrogen 65: gas was'-,in. mduced;; instead-of;- nitrosyl chloride, the re-.

It will be observed from Table. 1,6; that under; the con,-

ditions of the; NQCl exerte a; significa p ien nr he y aeewt. sfexidat entan up lem nt ry dizina eti nhro ghout: he; n ite; course of the oxidation.

listed-andatheatotalssuits. listed. nrTable; 3B wereobtained;

.'Z"al2le--3B [We lghtloss duliuepxidationnf.quinoline with H2804 -at.270 C; withlntroduetio'n ,of N at 1 litenper minute] Weight, Percent Elapsed Time Hours Loss, Parts Conversion In Table 30 below, sulfuric acid alone and nitrosyl chloride .alone the conversion of. quinoline by calculated from the ct theseatwo-efiectsare listed-.- The oxidation at:'240 with that. theoretically ascribable to i under comparable: conditions equations in,columns 3 and 4,- areactual conversion found is also listed together with the improvement in conversion over H 2SO4 alone and over the theoretical total of H250; and mtrosyl chloride.

Table 36 [Conversion in percent of quinoline during oxidation at 270 C. with 11:30.; alone and with introduction or NOCl at. 1 liter per minute] Total Improve- Improveits? an a te at n Min. o a z 4 core Thewy Found Theory alone cal Total The data listed in Table 3C indicate that under the conditions of the run NOCl exerts a promoter action in the early stages of the oxidation and exerts a supplementary oxidizing action throughout the course of the oxidation.

EXAMPLE 4 Still another oxidation of quinoline to nicotinic acid was carired out, in a manner identical with that employed in Example 1 except that the oxidation temperature was 300 C. with the results listed in Table 4A In a comparable run carried out at the same temperature as the above and in all respects identical with that described above except that nitrogen gas was introduced instead of nitrosyl chloride, at a rate of 1 liter per minute (instead of 0.5 liter per minute as in the above run) the results listed in Table 48 below were obtained.

Table 48 [Weight loss during oxidation of quinoline with H1804 at 300 C. with introduction of N; at 1 liter perminute] W h Elapsed Time Minutes Lossi fia its ogfiilii ion In Table 4C below, the conversion of quinoline by sulfuric acid alone and that theoretically ascribabie to nitrosyl chloride alone under comparable conditions as calculated from the equations in columns 3 and 4, are listed and the totals of these two effects are listed. The actual conversion found is also listed, together with the improvement in conversion over H2504 alone and over the theoretical total of H2804 and nitrosyl chloride.

Table 4C I [Conversion in percent of quinoline during oxidation at 300 C. with H2804 alone and with introduction of NOCl at 0.5 liter per minute] Total Improve Improveas o a 2 4 core Theory Found Theory alone cal Total 9. 5 35 44. 5 i2. 5 7. 5 2 19 51. 5 70. 5 7D. 7 19.2 +0. 2 28. 5 55. 5 S4. 0 84. 2 28. 7 +0. 2 33 60 98 91 31 -7 was introduced at 1 liter per minute.

The above table indicates that NOCI exerts a supplementary oxidizing action under the conditions of the run at 300 C. This temperature appears to be about the threshold temperature at or below which some promoter action may also be expected.

EXAMPLE 5 3-Picoline was oxidized to nicotinic acid in a manner identical in all respects to that described for quinoline under Example 1 except that 865 parts of a 6.5% solution of B-picoline in sulfuric acid was used as the charge and that NOCl was introduced at the rate of 1 liter per giilnute. The results of this run are listed in Table 5A e ow.

Table 5.4

[Weight loss and percent conversion of S-picoline during oxidation with B31810: }at 270 C. supplemented by NOCl introduced at 1 liter per m u e Weight Percent Elapsed Time, Minutes Loss, Conver- Parts sion 15 7 (gain) 11.7 30 10 22. 7 60 10 43. 8

In a run carried out in a manner identical in all respects to that described above except that nitrogen was introduced instead of nitrosyl chloride, the results listed in Table 5B below were obtained.

Table 58 [Weight loss and percent conversion of 3-picoline during oxidation with H3804 at 270 0. with introduction of N1 at 1 liter per minute] Weight Percent Elapsed Time Hours Loss, Paits Conversion In Table 5C below, the conversion of 3-picoline by 'sulfuric acid alone, and that theoretically ascribable to nitrosyl chloride under comparable conditions as calculated from the equations in columns 3 and 4, are listed and the totals of these two eiiects are listed. The actual conversions found in each case are also listed together with improvements in conversion over H2504 alone and over the theoretical total of H250; and nitrosyl chloride.

Table 5C [Conversion, in percent, of 3-picolino during oxidation at 270 C. with H1804 alone and with introduction of NOCl at 1 liter per minute} Tot Improve- Improve- Time, E 8 3 5 HzS 04+ Actual ment over ment over Min. Theo i N 001, Total H Theoretiry Theory alone cal Total The above data indicate that, under the conditions of the run NOCl exerts a supplementary oxidizing action.

on the oxidation of 3-picoline, but no promoter action.

EXAMPLE 6 3-Picoline was oxidized to nicotinic acid in a manner identical in all respects to that described for quinoline under Example 1 except that 875 parts of a 6.5% solution of 3-picoline in sulfuric acid was used as the charge and the oxidation was carried out at 300 C. and N001 this run are listed in Table 6A below.

The results of 1' Table 6A [Wfiight loss and percent conversion of 3-picoline during oxidation with 04 at 300 C. supplemented by N] introduced at 1 liter per minute] Weight Percent Elapsed Time Minutes Loss,,Parts Conversion In a run carried out in a manner identical in all respects with that described above except that nitrogen gas was introduced instead of nitrosyl chloride, the results listed in Table 68 below were obtained.

Table 6B [Weight loss and percent conversion during oxidation of 3-picoline with H 8 04 at 300 C. with introduction of N: at 1 liter per minute] Weight Percent Elapsed Tune Hours Loss, Parts Conversion Table 6C [Conversion. in percent, of 3-picoline during oxidation at 300 C. with H 04 alone and with introduction of N 0 G1 at 1 liter per minute] Total Improve- Improve- 0 a z 4 core Theory Found Theory alone cal Total The above table indicates that under the conditions of the run, NOCl exerts an appreciable supplementary oxidizing eifect on the H2804 oxidation of 3-picoline but no promoter action.

7 EXAMPLE 7 Isoquinoline was oxidized to cinchomeronic acid in a manner identical in all respects to that described for quinoline under Example 1 except that 890 parts of a 5.15% solutionof isoquinoline insulfurica'cid was used as the charge and the NOCl was introduced at the rate of 1 liter per minute. Results of this run are given in Table 7A below.

Table 7A [Weight loss and percent conversion ofisoquinoline during oxidation with H 80; ]at 270 C. supplemented by N 001 introduced at 1 liter per mm e Y 10 Table 17B [Weight loss and percent conversion oi-isoquinoline during oxidation with Hrs 04 at 270 C. with introduction of N2 at 1 liter per minute] Weight,

Percent Elapsed Time Hours Loss, Parts Conversion [Oonverslom in percent, of isoquinoline during oxidation at 270 C. with H 804 alone and with introduction of NO 01 at 1 liter per minute] Total Improve- Improve- Time, 5 01 gig Hrs 04+ Actual ment over ment over Min. F 6 NOC Total mso. Theoretieory oun Theory alone cal Total The above table indicates that under the conditions of the run NOCl exerts a consld'erable supplementary oxidizing action, and some promoter action on the H2504 oxidation of isoquinoline.

EXAMPLE 8 Z-methyl-S-ethyl pyridine (aldehyde collidine) was oxidized to nicotinic acid in a manner identical in all respects to that described for quinoline in- Example 1, except that 875 parts of a 5% solution of Z-methyl-S- ethyl pyridine in sulfuric acid was used as the charge.

Results of this run are given in Table 8A below.

Table 8A [Weight loss and percent conversion or 2-methyl-5-cthylpyridino during oxidation with H2804 at 270 C. supplemented by N001 introduced at 0.5 liter per minute] Weight Percent Loss, Parts Conversion Elapsed TimaMinutes moulmhco Oocnoul oooenww l"??? Table 83 [Weight loss and percent conversion during oxidation of 2-methyl 5-ethyl pyirlidinle with H98 04 at 270 C. with introduction of N: at 0.5 liter per in ute I I Weight, Percent w l ht P t Elapsed Hours Loss, Parts Conversion e g ercen Elapsed Time Minutes Loss, Parts Conversion In Table 8C below, the conversion of 2-methyl-5- In a run carried out in a manner identical in all respectsito that described above except that nitrogen was introduced instead of nitrosyl chloride, the results listed in Table 7B below were obtained.

ethyl pyridine by sulfuric acid alone, and that theoretically ascribable to nitrosyl chloride alone as calculated from the equations in columns 3 and 4, are listed and the totals of these two eflects are listed. The actual conversions found are also listed, together with improvements in i1 conversions over H2504 alone and over the theoretrical total of H2804 and nitrosyl chloride.

Table 8C [Conversion. in percent, of 2-methyl-5-ethy1 pyridine during oxidation at The above table indicates that under the conditions of the run, NOCl exerts a considerable supplementary oxidizing action and appreciable promoter action on the H2504 oxidation of 2-methyl-5-ethyl pyridine.

While the above describes .the preferred embodiments of my invention, it will be understood that departures may be made therefrom within the scope of the specification and claims.

l. A process for preparing pyridine carboxyhc acids which comprises subjecting a heterocyclic nitrogen compound containing a single pyridine nucleus, selected from the group consisting of quinoline, alkyl quinolines, isoquinoline, alkyl isoquinolines, 5- and S-hydroxy quinolines, 5- and S-nitroquinolines and the alkyl pyridines, dissolved in concentrated sulfuric acid to the action of nitrosyl chloride at a temperature between about 240 C. and about 300 C. in the presence of between about 0.5% and about 25 by weight, based on the weight of the nitrogen compound of a selenium-containing catalyst to convert the heterocyclic nitrogen compound to a pyridine carboxylic acid the quantity of sulfuric acid used being sufficient to provide at least a slight excess thereof over that required to form the nitrogen base sulfate, and to maintain such an excess during the oxidation reaction.

2. The process according to claim 1 wherein the heterocyclic nitrogen compound is isoquinoline.

3. A process for preparing pyridine carboxylic acids which comprises subjecting a sulfate of a heterocyclic nitrogen compound containing a single pyridine nucleus, selected from the group consisting of quinoline, aikyl quinolines, isoquinoline, alkyl isoquinolines, 5- and 8- hydroxy quinolines, 5- and S-nitroquinolines and the alkyl pyridines, dissolved in concentrated sulfuric acid r to the action of nitrosyl chloride at a temperature between about 240 C. and about 300 C. in the presence of between about 0.5% and about 25% by weight, based on the weight of the nitrogen compound, of a seleniumcontaining catalyst to convert the heterocyclic nitrogen compound to a pyridine carboxylic acid the quantity of sulfuric acid used being sufiicient to provide at least a slight excess thereof over that required to form the nitrogen base sulfate, and to maintain such an excess during the oxidation reaction.

4. A process for preparing pyridine carboxylic acids which comprises subjecting a heterocyclic nitrogen'compound containing a single pyridine nucleus, selected from the group consisting of quinoline, alkyl quinolines, isoquinoline, alkyl isoquinolines, 5- and 8-hydroxy quinolines, 5- and 8-nitroquinolines and the alkyl pyridines, dissolved in concentrated sulfuric acid to the action of nitrosyl chloride at a temperature between about 240 C. and about 300 C. in the presence of between about 0.5% and about 25 by weight. based on the weight of the nitrogen compound of a selenium-containing catalyst for a period between about 30 minutes and about 2 hours the quantity of sulfuric acid used being sufficient, to provide at least a slight excessthereof over that required to form the nitrogen base sulfate, and to maintain such an excess during the oxidation reaction.

5. The process of claim 1 wherein the heterocychc nitrogen compound is quinoline.

6. The process of claim 1 wherein the heterocychc mtrogen compound is 3-picoline.

7. The process of claim 1 wherein the heterocychc nitrogen compound is 2-methyl-5-ethyl pyridine.

8. In a process for accelerating the sulfuric acid oxidation of heterocyclic nitrogen compounds containing a single pyridine nucleus selected from the group consisting of quinoline, alkyl quinolines, isoquinoline, alkyl 1S0- quinolines, 5- and 8-hydroxy quinolines, 5- and S-nitroquinolines and the alkyl pyridines, the steps which comprise dissolving said heterocyclic nitrogen compound and between about 0.5 and about 25 by weight, based on the weight of the nitrogen compound a seleniumcontaining catalyst in concentrated sulfuric acid, and subjecting the resulting solution in the liquid phase to the action of gaseous nitrosyl chloride at temperatures between about 240 C. and about 300 C. to effect conversion of heterocyclic nitrogen base to pyridine carboxylic acid the quantity of sulfuric acid used being sufficient to provide at least a slight excess thereof over that required to form the nitrogen base sulfate, and to maintain such an excess during the oxidation reaction.

9. A process for producing an acceleration of the selenium catalyzed sulfuric acid oxidation of quinoline, greater than that theoretically ascribable to the combined action of the oxidizing agents used, which comprises subjecting said quinoline, dissolved in concentrated sulfuric acid, and in the presence of between about 0.5% and about 25% by weight, based on the weight of the quinoline, of a selenium-containing catalyst, to the action of nitrosyl chloride at a temperature of about 270 C. for a period of at least about 30 minutes, the quantity of sulfuric acid used being suflicient to provide at least a slight excess thereof over that required to form quinoline sulfate and to maintain such an excess during the oxidation reaction.

10. A process for producing an acceleration of the selenium catalyzed sulfuric acid oxidation of isoquinoline, greater than that theoretically ascribable to the combined action of the oxidizing agents used, which corn prises subjecting said isoquinoline, dissolved in concentrated sulfuric acid, and in the presence of between about 0.5% and about 25% by weight, based on the weight of the isoquinoline, of a selenium-containing catalyst, to the action of nitrosyl chloride at a temperature of about 270 C. for a period of at least about 30 minutes, the quantity of sulfuric acid used being sufficient to provide at least a slight excess thereof over that required to form isoquinolinc sulfate and to maintain such an excess during the oxidation reaction.

1l. A process for producing an acceleration of the selenium catalyzed sulfuric acid oxidation of 2-methyl-5- ethylpyridine, greater than that theoretically ascribable to the combined action of the oxidizing agents used, which comprises sub ecting said 2-methyl-5-ethylpyridine, dissolved 1n concentrated sulfuric acid, and in the presence of between about 0.5 and about 25 by weight, based on the weight of the 2methyl-5-ethylpyridine, of a selen um-containing catalyst, to the action of nitrosyl chloride at a temperature of about 270 C. for a period of at least about 30 minutes, the quantity of sulfuric acid used being sufiicient to provide. at least a slight excess thereof over that required to form Z-methyl-S-ethylpyridine sulfate and to maintain such an excess during the oxidation reaction.

No references cited.

Claims

1. A PROCESS FOR PREPARING PYRIDINE CARBOXYLIC ACIDS WHICH COMPRISES SUBJECTING A HETEROCYCLIC NITROGEN COMPOUND CONTAINING A SINGLE PYRIDINE NUCLEUS, SELECTED FROM THE GROUP CONSISTING OF QUINOLINE, ALKYL QUINOLINES, ISOQUINOLINE, ALKYL ISOQUINOLINES, 5- AND 8-HYDROXY QUINOLINES, 5- AND 8-NITROQUINOLINES, AND THE ALKYL PYRIDINES DISSOLVED IN CONCENTRATED SULFURIC ACID TO THE ACTION OF NITROSYL CHLORIDE AT A TEMPERATURE BETWEEN ABOUT 240* C. AND ABOUT 300* C. IN THE PRESENCE OF BETWEEN ABOUT 0.5% AND ABOUT 25% BY WEIGHT, BASED ON THE WEIGHT OF THE NITROGEN COMPOUND OF A SELENIUM-CONTAINING CATALYST TO CONVERT THE HETEROCYCLIC NITROGEN COMPOUND TO A PYRIDINE CARBOXYLIC ACID THE QUANTITY OF SULFURIC ACID USED BEING SUFFICIENT TO PROVIDE AT LEAST A SLIGHT EXCESS THEREOF OVER THAT REQUIRED TO FORM THE NITROGEN BASE SULFATE, AND TO MAINTAIN SUCH AN EXCESS DURING THE OXIDATION REACTION.