Patent GB-799754-A (GB)
Title: 3-alkyl substituted aliphatic dicarboxylic acids
IPC: C07C51/31
Filed: 1955-06-16
Abstract: A 3-alkyl substituted aliphatic dibasic carboxylic acid is obtained by partial air oxidation followed by nitric acid oxidation of an alkyl substituted cycloaliphatic hydrocarbon, the partial air oxidation being carried out in the liquid phase in the presence of a minor proportion by weight of a cycloaliphatic ketone, whereby substantially none of the cycloaliphatic hydrocarbon is converted into compounds having a combined carbonyl group, i.e. ketals and other compounds which hydrolyse to carbonyl in acid solution, removing from the air oxidation products unoxidized alkyl substituted cycloparaffin, and nitric acid oxidizing the alkyl substituted cycloparaffin-free air oxidation prouct to the 3-alkyl substituted aliphatic dibasic acid.  The cycloaliphatic ketone is preferably used in an amount of from 0.1 per cent to 1 per cent by weight of the alkyl substituted cyclohexane.  The alkyl substituted cyclohexane is preferably methyl cyclohexane but the methyl, ethyl, propyl, and higher straight and branched chain alkyl substituted cyclic hydrocarbons such as cyclopentane and cyclobutane can be used. The air oxidation step is preferably carried out at between 75 DEG  and 200 DEG  C. and at 50 to 500 pounds per square inch pressure and in the presence of an oxidation catalyst, e.g. a metal salt of an organic acid, e.g. cobalt naphthenate or cobalt stearate.  It is preferred that the air oxidation be limited to such an extent that only 1/2 to 2 mols. of oxygen reacts per mole of the cyclic hydrocarbon.  The unreacted hydrocarbon remaining after the air oxidation may be removed by distillation or steam distillation and may then be recycled to the air oxidation step.  The nitric acid oxidation is preferably carried out at elevated pressure in the presence of an oxidation catalyst.  The nitric acid oxidation may be effected in a single stage at between 30 DEG  and 150 DEG  C. and at a pressure between 15 and 500, e.g. from 50 to 500, pounds per square inch.  Alternatively, the nitric acid oxidation may be carried out in a two-stage continuous process, the first stage being operated in a circulating system at a temperature of between 40 DEG  and 90 DEG  C. under a pressure of 2-10 atmospheres with recirculation of the nitric acid.  The oxidation mixture is continuously withdrawn from the circulating stage at such a rate that the volume of the liquid mixture therein remains substantially constant and is conducted to the second nitric acid oxidation stage, preferably after being preheated, the mixture being maintained by cooling in this stage at between 90 DEG  and 120 DEG  C. for about 3 to 20 minutes, e.g. about 7 minutes.  The crude reaction product issuing from the second stage may be bleached by countercurrent treatment with air at between 70 DEG  and 100 DEG  C., the off gas from this operation being absorbed in water or nitric acid solution to recover the nitrogen oxides in the form of nitric acid.  When methyl cyclohexane is used in the process some monobasic acids, e.g. n-valeric and n-caproic acids, may also be formed in the process and these should be removed by fractional distillation prior to the crystallization of the 3-methyl adipic acid.  The oxidation catalyst in the nitric acid oxidation step may be an oxide or salt of a polyvalent metal, mixtures containing dissolved copper salts and dissolved vanadium or manganese salts being preferred.  An example is given for the two-stage oxidation of methyl cyclohexane to form 3-methyl adipic acid, appreciable amounts of glutaric, succinic, adipic and oxalic acid being also formed.  The air oxidation is conducted in two parts in the presence of cyclohexanone, cobalt carbonate being used as catalyst in one case and there being no catalyst in the second case. The products of both parts are then combined and after removal of unreacted methyl cyclohexane are oxidized with nitric acid in the presence of ammonium vanadate and copper wire to form the specified acids.  Specification 633,354 is referred to.