Aug. 19, 2010  2  US 2010/0210871 Al  to this problem, large amounts of these salts even have to be  disposed of with disposal costs.  [0014]  Another chemical process is the hydrolysis of  cyanohydrin with inorganic bases, for example sodium  hydroxide.  It  is likewise necessary here to release the alpha› hydroxycarboxylic acid by adding a mineral acid in stoichio› metric amounts. The hydrolysis of cyanohydrins likewise  goes to the stage of the ammonium salt with titanium dioxide  as the catalyst. The salt problem remains the same.  [0015]  Mono-, di- and tricarboxylic acids, and alpha- and  beta-hydroxycarboxylic acids, can be prepared fermenta› tively with the aid of microorganisms or enzymatically. This  affords the organic acids in the form of the ammonium salt.  They are released by adding the stoichiometric amount of a  mineral acid. In the case of di- or tricarboxylic acids, even  twice or three times the stoichiometric amount of a mineral  acid has to be added. This likewise gives rise to very large  amounts of ammonium salts, which in tum have to be  recycled in a complex manner or disposed of expensively.  [0016]  Processes in which no salt burden occurs are to date  uneconomic on the industrial scale for reasons of cost. One  example thereof is the esterification of an ammonium salt of  an alpha-hydroxycarboxylic acid with an alcohol and subse› quent hydrolysis of the ester with an acid catalyst  (JP7194387).  [0017]  In order to prepare free carboxylic acids from the  ammonium salts, there are various processes based on the  thermal decomposition of the ammonium carboxylates to  release ammonia (Scheme 1 ):  [0022]  U.S. Pat. No. 6,066,763 describes a process for pre› paring alpha-hydroxycarboxylic acids, which proceeds with› out the inevitable occurrence of large amounts of salts which  can be disposed ofonly with difficulty, ifat all. In this process,  the starting materials used are the ammonium salts of the  corresponding alpha-hydroxycarboxylic acids, said salts  being obtainable from the corresponding cyanohydrins with  the aid of enzymes (nitrilases). The salt is heated in the pres› ence of water and a solvent. Preferred solvents have a boiling  point of >40°  C. and form an azeotrope with water. The  distillative removal of the azeotropic mixture releases ammo› nia, which escapes in gaseous form via the condenser. The  corresponding alpha-hydroxycarboxylic acid accumulates in  the bottom of the distillation apparatus. However, the removal  of the water at elevated temperature results in large amounts  of the initially released alpha-hydroxycarboxylic acid being  converted by intra- or else intermolecular esterification to  dimers and polymers of the alpha-hydroxycarboxylic acid in  question. These subsequently have to be converted back to the  monomeric alpha-hydroxycarboxylic acid in question by  heating with water under elevated pressure. Another disad› vantage is the long residence times in both process stages.  They are 4 hours in the examples mentioned. Since the sol› vent is kept at boiling for the whole time in stage 1, the steam  consumption is uneconomically high. The cause of this is the  release of the alpha-hydroxycarboxylic acid, which becomes  more difficult with increasing depletion of ammonia.  It  does  not succeed 100%. After the end of the reaction, 3-4% bound  ammonia still remains in the bottoms. Under the reaction  conditions, another by-product which occurs is the corre› sponding amide of the alpha-hydroxycarboxylic acid, which  is only partly converted to the corresponding ammonium salt  by hydrolysis in stage 2 of the process (Scheme 2).  [0018]  According to GB967352, a small amount of water is  added to an ammonium salt of an unsaturated fatty acid, and  the mixture is heated at total reflux (80°  C.) or higher in  organic solvents in order to free or to remove ammonia to  obtain the unsaturated fatty acid.  [0019]  According to JP54115317, an organic solvent which  forms an azeotropic mixture with water is added to a 10-50%  aqueous solution of ammonium methacrylate, and the solu› tion which arises is heated to 60-100°  C. As a result, water is  distilled off as an azeotropic mixture and ammonia is  removed simultaneously in order to obtain free methacrylic  acid.  [0020]  According to JP7330696, a 10-80% aqueous solu› tion of an ammonium salt of an acidic amino acid is heated  with addition of water. Ammonia and water are distilled off  and the amino acid is released.  [0021]  In these processes, ammonia is in principle removed  easily, since the carboxylic acid has a high dissociation con› stant. In contrast, the degree of dissociation of ammonium  ions from ammonium salts of carboxylic acids with  pKa  values less than 4, for example sulphonic acids and alpha› hydroxycarboxylic acids, is low.  It  is therefore very difficult  to remove ammonia from the salts of strong acids. In order to  remove the majority of ammonia, a long period is required, or  it is necessary to add a large amount of water or of organic  solvents. In the abovementioned processes, 50% or more of  the corresponding carboxylic acid remains as the ammonium  salt.  [0023]  The alpha-hydroxycarboxylic acids obtained pos› sess only a purity of approx. 80%, and so a further purification  by means ofliquid-liquid extraction or crystallization is usu› ally necessary.  [0024]  In patent publication WO 00/59847, the ammonium  salt solutions of the alpha-hydroxycarboxylic acids are  brought to a concentration of >60% under reduced pressure.  The conversion to dimeric or polymeric esters of the corre› sponding alpha-hydroxycarboxylic acids is intended to be  less than 20%. Passing a gas through, preferably steam,  releases and drives out ammonia. Using the example of2-hy› droxy-4-methylthiobutyric acid, 70% free acid is achieved;  the remainder consists of the unconverted ammonium salt of  2-hydroxy-4-methylthiobutyric acid and the corresponding  dimeric ester.  [0025]  US 2003/0029711 Al describes a process for  obtaining organic acids, including from aqueous solutions of  the ammonium salts, with addition of a hydrocarbon as an  entraining agent. Heating the mixture affords a gaseous prod› uct stream which comprises an azeotrope consisting of the  organic acid and the entraining agent. In order to isolate the  acid from this product stream, further steps such as conden› sation and additional distillations must be carried out. Fur› thermore, this process also requires the addition of additional  &heme_J_  R-coo- NILt - R-COOH + NH3  &heme--2 