3,701,804 United States Patent Office Patented Oct. 31, 1972 2 vention may be varied widely since at least some adipic 3,701,804 acid and acetic acid will be formed even at 100:1 or 1:100 PROCESS FOR ADPC ACD MANUFACTURE molar ratios, respectively. For practical yields, it is pre Walter H. Knoth, Jr., Mendenhali, Pa., and George W. Parshall, Wilmington, Del, assignors to E. I. du Pont ferred to employ ratios between 3:1 and 1:15, and best de Nemours and Company, Wilmington, Del. yields are obtained when the respective molar ratios are No Drawing. Filed Mar. 19, 1971, Ser. No. 126,345 between 1:1 and 1:5. Int, C, CO7 55/14 For the reaction to proceed economically, there should U.S. C. 260-530 R 5 Claims be present at least an equivalent amount and preferably a slight molecular excess of oxygen. Excess oxygen up to O 100 fold may be employed but there is no advantage in ABSTRACT OF THE DISCLOSURE extremely high oxygen proportions. Oxygen may be Disclosed herein is a process for the manufacture of supplied to the reaction in the form of pure oxygen gas adipic acid, a reactant in the preparation of 6,6 nylon, or in a gas mixture containing substantial quantities of comprising reacting cyclohexene and acetaldehyde in the OXygen along with inert materials as in air. presence of oxygen and a catalyst consisting of a salt of 5 The metal catalyst is reduced in Equations 4 and 5 one of the metals vanadium, tungsten, molybdenum, above but under the reaction conditions it is rapidly re osmium or ruthenium, said process optionally employing oxidized. The catalyst may be any compound of the select a cocatalyst consisting of an inorganic nitrogen-containing ed metals in which the metal is capable of facile valence compound. change. The metal compound supplied to the reaction 20 may contain the metal in any of its positive valence states. The amount of catalyst, expressed as metal, can range BACKGROUND OF THE INVENTION from 0.001 to 10% of the weight of the reaction mixture (1) Field of the invention of cyclohexene and acetaldehyde. It is preferably in the range of 0.01 to 5% of this weight. This invention concerns a new process for the prepara 25 Some of the primary catalytic compounds contemplated tion of adipic acid in which acetic acid is a desirable to be employed alone or in combination are listed below. secondary product. Vanadium: ammonium meta-vanadate, vanadium ace (2) Description of the prior art tylacetonanes, vanadyl acetylacetonate, vanadium, pentox ide, vanadic acid, the metal vanadates, vanadium oxychlo The nitric acid oxidation of cyclohexene to adipic acid 30 ride, vanadyl naphthenate, vanadyl dichloride, vanadyl with vanadium catalysis is known. See: U.S. Pat. 2,323, sulfate; 861, British Pat. 1,068,905, French Pat. 981,609, and J. Tungsten: tungstic acid and its salts such as sodium Franz and W. Knowles, Chem. and Ind., 1961, 250. These and lithium tungstate, sodium phosphotungstate, sodium prior art processes, quite distinct from the novel process tungstosilicate, tungsten dioxide, tungsten trioxide, tung taught herein, suffer from the disadvantage of having 35 sten pentoxide, tungsten oxydichloride, tungsten oxytetra reaction systems containing extremely corrosive nitric chloride; acid. Molybdenum: ammonium molybdate, sodium molyb SUMMARY AND DETAILS OF THE INVENTION date, molybdenum dioxide, molybdenum trioxide, molyb Cyclohexene and acetaldehyde are reacted in the pres 40 denum pentoxide, molybdenum sesquioxide, sodium phos ence of oxygen and a primary catalytic compound of one phomolybdate, molybdenum oxydichloride, molybdenum of the metals vanadium, tungsten, molybdenum, osmium oxytrichloride, molybdenum oxytetrachloride; or ruthenium to form adipic acid and acetic acid. Osmium: osmium monoxide, osmium dioxide, osmium Although it is desired not to be bound to any theory tetroxide, osmium sesquioxide, potassium osmiate; concerning the mechanism of reaction, it is believed that 45 Ruthenium: ruthenium dioxide, ruthenium tetroxide the following equations represent the major reaction and ruthenium nitrate. paths: Some of these catalytic compounds contain the metal in its catalytically active state. In others the metal is oxi 1. CHCHO - O - CH3COOOH acetaldehyde peracetic acid dized under the reaction conditions to a catalytically active 50 form. 2. An inorganic nitrogen-containing cocatalyst can be em N ployed to aid in the reoxidation of spent metal catalyst. CHCOOOH -- - CH3COOH -- jo Said cocatalyst can be one or more inorganic metal ni trate(s) and/or nitrogen oxide(s). The inorganic ni cyclohexene acetic acid cyclohexene acid trate(s) may be any metal nitrate(s), however, alkali 55 metal nitrates and alkaline earth metal nitrates are pre 3. OH ferred. Particularly preferred are lithium, sodium and po O -- CH3COOH - tassium alkali metal nitrates and magnesium and calcium OCOCH alkaline earth metal nitrates. Operable nitrogen oxides in 60 clude NO, NO, NO3, NO2, NO, and NO. The amount 2-acetoxycyclohexanol of cocatalyst(s) used may be up to 300% by weight of 4. the metal in the primary catalyst. OE O The process of this invention may be carried out over --> CH3COOH -- (CH2)(COOH) a wide temperature range, particularly from -20° to 200 oCoCE, catalyst adipic acid C. Preferred temperatures are in the range from 15° to 125 C., temperatures of up to about 60° C. being pre 5. ferred with, vanadium catalysts and temperatures over 60 O O - (CH2)4(COOH)2 C. being preferred with tungsten, molybdenum, osmium catalyst adipic acid and ruthenium catalysts. Pressure is not a critical variable in the process of this The proportions of cyclohexene and acetaldehyde invention and pressures both above and below atmos which may be brought together in the process of this in pheric may be employed. Preferred pressures are in the 3,701,804 3 4 range from 1 to 60 atmospheres, and particularly pre fallen to about 30 p.s.i.g.; however, this did not seem to ferred are pressures in the range from 1 to 15 atmos affect the results. pheres. When air is used as the oxidant, it is customary After the reaction period, excess pressure was vented to employ pressures up to about 2 times those correspond slowly at ambient temperature, and a weighed amount of ingly employed with pure oxygen. is toluene or xylene was added to serve as a standard for The reaction of this invention is usually essentially com- quantitative gas chromatographic analysis. The crude plete within a period of 1-20 hours. Longer periods are mixture was then analyzed for the volatile constituents, permissible and shorter periods (to a minimum of 15 including recovered acetaldehyde, cyclohexene, acetic acid minutes) may be used with some sacrifice in yield. and 2-acetoxycyclohexanol, by gas chromatography on a The addition of a liquid reaction medium in the proc- 10 Varian Aerograph Series 1700 instrument. The gas chro ess of this invention is not essential since the reaction can matographic columns were stainless steel (6' x 4') and be carried out neat. If desired, a liquid which is relatively were packed with 20% Triton6 X305 (octylphenoxy oxidation-resistant, such as acetic acid, ethyl acetate, ben- polyethylene glycol) on 60-80 mesh Chromosorbë “W' Zene, tertiary butanol or water may be employed as a Regular (diatomaceous earth which has been flux-calcined diluent. 15 with sodium carbonate and then waterwashed). The col umns were programmed from 80-200 C. at 6 C./min PREFERREP EMBODIMENTS OF ute with an injector temperature of 180 C. THE INVENTION For detection of the carboxylic acids formed in the The following nonlimiting examples are meant to illus- experiment, the readily yolatile materials were removed trate the invention. Percentages are by weight and stirring 20 under reduced pressure from the remainder of the crude is maintained throughout the reaction period. All yield reaction product. A known amount of heptanoic, pimelic figures are based on cyclohexene charged. Examples 2, or azelaic acid was added to the residue to serve as a 20, 25, 27 and 31 have been included for comparative standard for gas chromatographic analysis. The reaction purposes. mixture was then treated by one of two procedures (A EXAMPLE 1. 25 or B, below), both designed to convert all of the car boxylic acids present to their methyl esters, which are Acetic acid (1 ml.), acetaldehyde (2 ml.), cyclohexene sufficiently volatile to detect and measure by gas chroma (1 mi.) and ammonium metavanadate, NHVO (0.1 g.) tographic analysis. were charged to a 375-ml. glass pressure bottle. This was The following analytical procedures were employed in chilled to about 78° C. and flushed with oxygen. It was 80 the manner described to determine the content of the then pressured to 50 p.s.i.g. with oxygen and heated to reaction products made herein. Procedure A was employed 60° C. at autogenous pressure. A leak developed after to determine the products in Examples 1 and 3 and Pro 15 minutes and little pressure could be maintained for cedure B was employed to determine the products in Ex the remainder of the reaction period (1.75 hours). De- amples 2 and 4 to 39. spite this, analysis of the product revealed a desirably 8 Procedure A-Ten milliliters of a 10% solution of high 4:1 ratio of adipic acid to glutaric acid (by-product). boron trifluoride in methanol was added to the evapora tion residue containing the reference acid. The mixture EXAMPLES 2 TO 19 was heated on a steam bath for two minutes and then 40 diluted with 30 ml. of water followed by three extrac These examples are presented in Table 1. Example 2 tions with 30 ml. portions of hexane. The extracts were therein shows the inferior results obtained in the absence combined, concentrated to about 4 ml.