Acids mandelic

Mandelic acid and its derivatives are utilized as convenient precursors for the introduction of a chiral center, and they possess the extra advantage of bearing a useful functional group. Many mandelic acid derivatives also act as chiral auxiliaries for the induction of a chiral center in stereoselective transformations. Numerous natural products, such as macrolides and ionophore antibiotics, possess a carbon framework that may be viewed synthetically as arising from a sequence of highly stereo- and enantioselective aldol condensations. Boron enolates, chiral auxiliaries derived from mandelic acids 1 or 2, provide remarkably high aldol stereoselectivity. 

Catalytic hydrogenation of 1 in the presence of rhodium on aluminum oxide proceeds smoothly to afford (5)-hexahydromandelic acid (3) [2]. Subsequent treatment of 3 with ethyllithium provides in 75% yield the ketone 4, which is 0-silylated to afford 5. Generated in situ with the appropriate dialkylboron triflate and 5, the boron enolates 6a—c react with a variety of aldehydes to provide exclusively a mixture of syn-d o products 7 and 8 in 70-80% yields, often with excellent stereoselectivities. 

Preparation of the left-hand fragment, which incorporates the C-11 to C-13 portion of 18, utilizes the aldol reaction of / -boron enolate 10 with propionaldehyde to provide the a-hydroxy acid 11 in 85% yield and 100 1 stereoselectivity. Subsequent diazomethane esterification, O-silylations, DIBAL reduction, and Collins oxidation affords the optically pure aldehyde 12 in an overall yield of 75%. 

The aldol methodology described is useful for the preparation of diastereomerically pure syn aldol products. Preparation of the corresponding a /-3-hydroxy-2-methylcarbonyl aldol products can be achieved utilizing a -yw-intermediate that possesses two different functional groups, an olefin and an ester, both of which can be appropriately modified to achieve the 

Tylonolide hemiacetal (33), the aglycone of the antibiotic tylosin, possesses an anti 14-hydroxymethyl-15-acyloxy stereochemistry conveniently contained in 26, which may be viewed as the western half of 33. In order to prepare the eastern half of 33, an aldol reaction leading to the desired syn stereochemistry at C-3 and C-4 is exploited. The reaction of achiral aldehyde 27 with the S-boron enolate 28 proceeds with the expected diastereofacial selectivity to provide, in a combined yield of 80% after O-silylation, a separable mixture of 29 (derived from the / -enantiomer of 27) and 30 (from the S-enantiomer of 27). Subsequent functional group transformation of 30 ultimately leads to the a-(TMS)methylketone 31. The anion of 31, generated with lithium hexamethylsilazide in THF at — 78 °C, undergoes a Peterson condensation with 26 to afford in 60% yield the seco-diC d 32. Treatment of 32 with 70% acetic acid at 85 °C for one hour affords 33 in 60% yield. The attractive feature of this 

Place 10 g. of clean sodium (cut into small pieces) in a 500 ml. round-bottomed flask fitted with a double surface reflux condenser. Introduce 100 g. (127 ml.) of absolute ethyl alcohol and allow the reaction to proceed as vigorously as possible if the alcohol tends to flood the condenser, cool the flask momentarily with a wet towel or by a stream of cold water. When all the sodium has reacted, add 40 g. of pure phenol. Distil off the 

In a 4-I. wide-mouthed glass jar, fitted with a mechanical stirrer, is placed a solution of 150 g. (3 moles) of sodium cyanide (Note i) in 500 cc. of water and 318 g. (3 moles) of u.s.P. benz-aldehyde. The stirrer is started and 850 cc. of a saturated solution of sodium bisulfite (Note 2) is added to the mixture, slowly at first and then in a thm stream. The time of addition is ten to fifteen minutes. During the addition of the first half of this solution, 900 g. of cracked ice is added to the reaction mixture, a handful at a time. The layer of mandelonitrile which appears during the addition of the sulfite solution is separated from the water in a separatory funnel. The water is extracted once with about 150 cc. of benzene, the benzene is evaporated, and the residual mandelonitrile is added to the main portion. 

The crude nitrile (about 290 cc.) is placed at once (Note 3) in a 25 cm. evaporating dish, and 425 cc. of c.p. concentrated hydrochloric acid (sp. g. 1.19) is added. The hydrolysis is allowed to proceed in the cold (Note 4) for about twelve hours, after which the mixture is heated on a steam bath to remove the water and excess hydrochloric acid. After heating for five to six hours it is advisable to cool the mixture (Note 5) and 

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

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). 

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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... 

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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