Acid methanolysis

The GC-MS chromatogram obtained with the same substance after acid methanolysis and silylation is presented in Figure 10.10. The major compounds are fatty acid methyl esters corresponding to a mixture of an animal fat (attested by the presence of E15 0 and E17 0 with ante and iso isomers) and castor oil (attested by the presence of methyl ricinoleate E18 1,120H) [32]. Diterpenoid or triterpenoid resin components are not observed. 

ACH (1) [Acetone cyanhydrin] A process for making methyl methacrylate via this intermediate. Acetone reacts with hydrogen cyanide to yield the cyanhydrin. This is then converted to methacrylamide, using concentrated sulfuric acid. Methanolysis of this yields methyl methacrylate. Developed by Rohm GmbH Chemische Fabrik, Germany, and ICI, UK used in 11 countries in 1990. 

Hemicelluloses Pulp fibres 1% Acid methanolysis with HC1, followed GC FID n.r. n.r. 38... 

Oxidation of the retrain dm-oxazolo[3.2-/,) isoxazolc 119 followed by a spontaneous fragmentation of the transient A-oxide resulted in the nitrone intermediate 120. Acidic methanolysis of this latter liberated the /5-hydroxy ketone 121 (Equation 52) <1995JOC1720>. 

D-Galacturonic acid (Methanolysis) a-Furanoside formed exclusively at outset. At equilibrium a-furanoside, 11% P-furanoside, 36% a-p5rranoside, 36% p-pyranoside, 17% Furanosides are notably more prevalent at equilibrium than is the case with galactose (22%). Six-membered rings are apparently disfavoured by having the carboxylic acid group attached directly 14)... 

The deprotection of N-formylamines 30 to the free amines can be achieved easily by acidic methanolysis. For the N-formylamide 30b, it was shown that the deprotection proceeds quantitatively and without racemization. 

Methoxyneuraminic Acid (crystalline) By acid methanolysis of brain glyco-lipids (and later BSM)... 

Trimethylorthoformate 17 is a highly activated Cl building block and a formic acid equivalent which is commonly applied in organic condensation reactions. 17 can be produced on an industrial scale by two major routes. The first starts with chloroform and sodium methanolate, but produces 3 equiv. of sodium chloride as waste. The second route is based on the acidic methanolysis of cyanhydric acid, which also produces stoichiometric amounts of ammonium chloride. Despite the reduced salt waste, the use and handling of cyanhydric acid mean high safety costs. Therefore, anodic methoxylation of formaldehyde dimethylacetal (16) to... 

Formamidines such as 81 may be lithiated with s-BuLi or r-BuLi and give stabilised organolithiums 82 which react with a wide range of electrophiles. Cleavage is much easier than cleavages in the amide series acidic methanolysis gives a secondary amine 83 while hydride reduction gives a tertiary amine 84.57... 

The fatty acid content of the ovipositor tips of a variety of Lepidopteran species were determined by acid methanolysis followed by gas-liquid chromatography (GLC) (4.). In each case, unusual fatty acids corresponding to pheromone components were identified. For example, the tufted apple bud moth, Platynota idaeusalis, uses (E)—11—tetradecenyl acetate and alcohol as pheromone components (5.) and also contains (E) -11—tetradecenoic acid in its ovipositor tip. In several species, the fatty acid content of the rest of the insect also was determined. In each instance, the unusual fatty acid components were found only in the ovipositor tip or in the pheromone-producing gland located in the tip. 

Preparative Methods a ca. 1 1 mixture of cis- and trans-B-methoxy-2,5-dimethylborolanes is first obtained by reaction of the Grignard reagent derived from 2,5-dibromohexane with diethylaminodichloroborane, followed by acidic methanolysis (eq 1). ... 

The isomeric methyl 3,6-dideoxy-3-C-methylhexofuranosides 230 and 232 (Scheme 13.71) were derived from (S )-2-benzyloxypropanal via homoaldol reactions in three steps. Addition of a-titanated ( -2-butenylcarbamate ( )-226 to (S )-2-benzyloxypropanal gives in 80% yield a 53 47 mixture of enantiomerically pure (Z)-3,4-antiadducts 227 and 228. These are separated by chromatography on silica gel. Face-selective epoxidation of 227 yields 229, the acidic methanolysis of which forms 230. Similarly, adduct 228 is converted into epoxide 231 and then into methyl furanoside 232 in high yield [128]. 

By applying a similar approach, Wu and coworkers [135] observed a highly double-stereoselective hetero Diels-Alder addition between diene 245 and ethyl glyoxylate. This reaction was catalyzed by the (salen)Co° complex 246 (Scheme 13.75). The major adduct 247 is hydroborated to give alcohol 248. Stereochemical inversion is achieved via oxidation and subsequent reduction to 249. Acid methanolysis followed by diol protection furnishes 250. Quenching of the lithium enolate of 250 with phenyl disulfide and subsequent oxidation with A-bromosuccinimide forms, after deprotection, (-f)-KDO (3-deoxy-D-mann6>-oct-2-ulosonic acid) [136a]. 

GC is usually used when sugars in the saponins must be determined acid methanolysis of the glycosides and subsequent GC analysis of the resulting persilylated methyl sugars (derivatives with higher volatility) provide information on the nature and ratio of the sugars. Today, with the aid of the newer spectroscopic tecniques, GC is not so much utilized. 

Acid methanolysis of the glycosides and subsequent GLC analysis of the resulting persilylated methyl sugars provided information on the nature and ratio of the sugars ... 

The abnormally selective acid methanolysis is apparently due to stabilization of the intermediate transitory carbonium ion by resonance (p. 42). 

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