Mandellic acid

Mandelic acid. This preparation is an example of the synthesis of an a-hydroxy acid by the cyanohydrin method. To avoid the use of the very volatile and extremely poisonous hquid hydrogen cyanide, the cyanohydrin (mandelonitrile) is prepared by treatment of the so um bisulphite addition compound of benzaldehj de (not isolated) with sodium cyanide ... 

It is important to mix the mandelonitrile with hydrochloric acid immediately it has been separated from the water. Standing results in rapid conversion to the acetal of benzaldehyde and mandelonitrile C(H,CH[OCH(CN)C H,] and/or the iso-nitrile the yield of mandelic acid will, in consequence, be reduced. 

The phenylacetic acid derivative 469 is produced by the carbonylation of the aromatic aldehyde 468 having electron-donating groups[jl26]. The reaction proceeds at 110 C under 50-100 atm of CO with the catalytic system Pd-Ph3P-HCl. The reaction is explained by the successive dicarbonylation of the benzylic chlorides 470 and 471 formed in situ by the addition of HCl to aldehyde to form the malonate 472, followed by decarboxylation. As supporting evidence, mandelic acid is converted into phenylacetic acid under the same reaction conditions[327]. 

Analyses of alloys or ores for hafnium by plasma emission atomic absorption spectroscopy, optical emission spectroscopy (qv), mass spectrometry (qv), x-ray spectroscopy (see X-ray technology), and neutron activation are possible without prior separation of hafnium (19). Alternatively, the combined hafnium and zirconium content can be separated from the sample by fusing the sample with sodium hydroxide, separating silica if present, and precipitating with mandelic acid from a dilute hydrochloric acid solution (20). The precipitate is ignited to oxide which is analy2ed by x-ray or emission spectroscopy to determine the relative proportion of each oxide. 

L-Menthol [2216-51-5] (75) and D-menthol [15356-70-4] have been used as chiral auxiharies in the synthesis of optically active mandehc acids. Reduction of (-)-menthol ben2oylfomiate (76) with a stericaHy bulky reducing agent, ie, sodium bis(2-methylethoxy)aluminum hydride (RED-Al), followed by saponification, yields (R)-mandelic acid (32) of 90% ee. 

Zirconium is often deterniined gravimetrically. The most common procedure utilizes mandelic acid (81) which is fairly specific for zirconium plus hafnium. Other precipitants, including nine inorganic and 42 organic reagents, are Hsted in Reference 82. Volumetric procedures for zirconium, which also include hafnium as zirconium, are limited to either EDTA titrations (83) or indirect procedures (84). X-ray fluorescence spectroscopy gives quantitative results for zirconium, without including hafnium, for concentrations from 0.1 to 50% (85). Atomic absorption determines zirconium in aluminum in the presence of hafnium at concentrations of 0.1—3% (86). 

Maltol — see Pyran-4-one, 3-hydroxy-2-methyl-Maltol, ethyl — see Pyran-4-one, 3-ethoxy-2-methyl-Maltol, methyl — see Pyran-4-one, 3-methoxy-2-methyl-Mandelic acid ethyl ester, 1, 310-311 Manganaindene reactions, 1, 671 Mannich bases dehydro... 

Either of two methods may be used to extract the mandelic acid from the ammonium chloride. 

A. Extraction with Benzene.—The mandelic acid is separated from the ammonium chloride by extraction with hot benzene. This is best done by dividing the solid mixture into ten approximately equal parts (Note 7). One of these portions is placed in flask with i 1. of boiling benzene. After a few minutes the hot benzene solution is decanted through a suction funnel (Note 8). The filtrate is cooled in an ice bath and the mandelic acid that crystallizes is filtered with suction. The benzene is returned to the extraction flask containing the residue from the first extraction, and a new portion of the ammonium chloride-mandelic acid mixture is added and extracted as before. The process is repeated until the mandelic acid is completely removed from the ammonium chloride (Note 9). 

The yield of pure white mandelic acid melting at 118° is 229-235 g. (50-52 per cent of the theoretical amount based on benzaldehyde). 

The mandelonitrile should be mixed with hydrochloric acid as soon as it is separated from the water. Wood and Lilley (7. Ghent. Soc. 127, 95 (1925)) have found that it undergoes rapid rearrangement to the isonitrilc. Hence if it is allowed to stand long before the hydrolysis, the yield of mandelic acid is reduced. 

If the crude product is not first washed with cold benzene the final product is usually colored. Very little mandelic acid is lost by this washing. 

The entire amount of the ammonium chloride-mandelic acid mixture may be boiled with the benzene but this gives a supersaturated solution of the acid in the benzene and much difficulty is met in the filtration. The solubility of mandelic acid in hot benzene is approximately i g. in 50 cc. 

The funnel should be previously heated and have fairly large holes so as not to be clogged by the mandelic acid that begins to crystallize as soon as the solution cools slightly. Only a slight suction should be applied during filtration. 

Usually two or three extractions of the ammonium chloride residues after the addition of the last portion of the crude mixture are necessary in order to obtain all of the mandelic acid. On concentrating the benzene used for the extraction, about 5 g. of impure mandelic acid may be obtained. To diminish mechanical losses it is recommended that the same container be used to collect and crystallize the several filtrates. 

The ether extraction method (B) is quicker, especially when several runs are to be made. Mandelic acid is obtained in the same yield by this method. The benzene extraction may be better for small preparations, or when a single run is to be made. 

The mother liquors are worked up for toluene, but it is not profitable to try to recover the small amount of impure mandelic acid which they contain. 

Mandelic acid is best prepared by the hydrolysis of mandeloni-trile with hydrochloric acid. The mandelonitrile has been prepared from amygdalin, by the action of hydrocyanic acid on benzaldehyde, and by the action of sodium or potassium cyanide on the sodium bisulfite addition product of benzaldehyde. ... 

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