Patent GB-408834-A (GB)
Title: Improvements in the manufacture of hydroxy dicarboxylic acids
IPC: C07C51/16
Filed: 1933-06-22
Abstract: <PICT:0408834/IV/1> Hydroxy carboxylic acids or salts thereof, such as tartaric acids and their salts, are obtained by the oxidation of a dicarboxylic acid or an acid salt thereof having an ethylene structure, such as fumaric or maleic acids or maleic anhydride, in the presence of a catalyst, e.g. osmic acid, and in a liquid medium in which the ratio of dicarboxylic acid to liquid medium is initially greater than 1 : 10 and preferably about 1 : 4 or 1 : 5, or in a liquid medium comprising a concentrated solution of the acid to be produced.  Sodium chlorate is the preferred oxidizing agent, and the process may be carried out continuously or intermittently and preferably at temperature of about 40 DEG --55 DEG  C. As the conversion proceeds, more oxidizing agent and dicarboxylic acid, which is relatively insoluble, are added, and tartaric acid gradually crystallises out.  Evolved vapours are passed through a saturated solution of fumaric acid to recover osmic acid.  The accumulated solid tartaric acid is separated from the mother liquor, washed with a solvent, e.g. benzene or carbon tetrachloride, to recover osmic acid and purified.  The osmic acid solution is purified by treatment with an alkali and hydrochloric acid and added to the saturated solution of fumaric acid and the mother liquor, thus forming the medium for further conversion. The mother liquor may be used until the accumulation of impurities, such as sodium chloride, becomes too great, when the osmic acid is recovered by extraction with an organic solvent and used for a succeeding reaction.  The tartaric acid remaining in the mother liquor is precipitated by the addition of potassium carbonate and recovered as the potassium salt.  The final traces may be obtained as calcium tartrate by neutralization with calcium carbonate.  An apparatus for the continuous method of working is shown in Fig. 1, having two compartments 1 and 2 provided with stirring means such as propellers 5, 5<1> and 6, 6<1> and coils 18 and 21 for heating or cooling the reaction mixture. Openings 10, 11, 12 and 13 are provided for the introduction of reactants and openings 14, 15, 16 and 17 for the escape of evolved gases.  The two compartments are separated by perforated sheets 9 which are arranged to permit or prevent communication between them, and the whole device is mounted at its axis so that either compartment may be turned to the uppermost position.  The reaction may be carried out as previously described by reacting 1 part of fumaric acid, 4 parts water, 0.5 part of sodium chlorate and 0.004 part of osmic acid in compartment 1.  When the desired amount of tartaric acid separates out, the mother liquor is filtered into the lower compartment and the acid washed by spray 7.  The perforations 9 are then closed, the compartments reversed in position, the concentration of osmic acid restored and further reactants are added through opening 13.  This procedure is repeated until the accumulation of impurities in the mother liquor becomes too great.  The separated tartaric acid in the lower compartment is washed with carbon tetrachloride or benzene, to remove osmic acid.  The solution is discharged through opening 14 and treated to recover osmic acid, and the crystalline tartaric acid removed through opening 10 and subsequently purified.  In a modified form of apparatus, the lower compartment is replaced by a chamber connected with the reaction chamber through a pump and reservoir.  In operation, the mother liquor is filtered into the chamber and pumped into the reservoir where it is retained until the tartaric acid is emptied into the lower chamber.  The mother liquor is then fed to the reaction chamber for further reaction, meanwhile the tartaric acid is washed in the lower compartment to remove osmic acid as before and then removed for purification.  Maleic acid is converted into meso-tartaric acid and fumaric acid into dl-tartaric acid.  In the conversion of the former, the formation of chlorine should be avoided since this causes the formation of fumaric acid and consequent contamination of the meso-tartaric acid.  Other suitable catalysts include compounds of ruthenium, vanadium, iron, or manganese.  Other compounds of osmium such as the lower oxides, osmium trichloride and tetrachloride and complex salts, e.g. with potassium chloride, may also be used.  Mixtures of the above compounds may also be used. Other oxidizing agents may also be used, e.g. other salts of chloric acid, salts of perchloric and hypochlorous acids and also the free acids, other per-acids and their salts, hydrogen peroxide and inorganic or organic peroxides.