Pyridines esterification

Procedure Amines, 10-1000 jug, were acetylated by treatment with 10-20 All of redistilled acetic anhydride and 10-20 /rl of pyridine (distilled over potassium hydroxide). Excess reagents were removed in a vacuum desiccator. Methyl esters of amine acids were prepared by refluxing in methanolic hydrogen chloride. iV-Acetylation of these esters was by treatment with acetic anhydride and pyridine. Esterification of other acids was carried out with diazomethane in ether. The products were dissolved in ethyl acetate, and volumes of 0.1 to 2 ju.1 were injected into the gas chromatograph. Amounts of sample injected were about 0.1 jitg for rapidly eluted compounds and 1 p,g for those with long retention times. In some cases, acetone condensation products of the primary amines were chromatographed. Catecholamines, however, underwent decomposition under these conditions. 

Esterification with acyl chlorides (Section 15 8) Acyl chlorides react with alcohols to give esters The reaction is usually carried out in the presence of pyridine... 

Several derivatives of cellulose, including cellulose acetate, can be prepared in solution in dimethylacetamide—lithium chloride (65). Reportedly, this combination does not react with the hydroxy groups, thus leaving them free for esterification or etherification reactions. In another homogeneous-solution method, cellulose is treated with dinitrogen tetroxide in DMF to form the soluble cellulose nitrite ester this is then ester-interchanged with acetic anhydride (66). With pyridine as the catalyst, this method yields cellulose acetate with DS < 2.0. 

Acetyl (79GEP2808070,71FES1074) and Other groups on the pyridine ring have been oxidized to the corresponding carboxylic acids in the pyrido-[2,3-c]- and -[3,4-d]-pyridazine fields. Acid groups in pyridopyridazines behave normally on esterification (66CPB1010). 

As with poly(vinyl alcohol), poly(vinyl cinnamate) is prepared by chemical modification of another polymer rather than from monomer . One process is to treat poly(vinyl alcohol) with cinnamoyl chloride and pyridine but this is rather slow. Use of the Schotten Baumann reaction will, however, allow esterification to proceed at a reasonable rate. In one example poly(vinyl alcohol) of degree of polymerisation 1400 and degree of saponification of 95% was dissolved in water. To this was added a concentrated potassium hydroxide solution and then cinnamoyl chloride in methyl ethyl ketone. The product was, in effect a vinyl alcohol-vinyl cinnamate copolymer Figure 14.8)... 

When yohimbine is heated with potash solution it is eonverted into potassium yohimbate, from which yohimbic acid (the forms yohimboie and yohimboaic are also used and noryohimbine), C20H24O3N2. H2O, is liberated by acetie acid it crystallises from water in lustrous prisms, m.p. 269° or 299° (dry, dec.), [ajo 138-8° (pyridine), and, on esterification with methyl alcohol and its homologues, reproduces yohimbine and its homologues, analysis of which by Field confirmed the view that yohimbine is methyl yohimbate, and has the formula assigned to it by Fourneau and Page. ... 

Enol esterification with acetyl chloride-acetic anhydride gives the A -trien-3-acetate, but reaction with isopropenyl acetate or with hot acetic anhydride-pyridine gives A " -trien-3-acetates. " Since A"" -3-ketones react with Girard reagents, these linear dienones can be separated from A ""-3-ketones. ... 

Esterification A solution of 500 mg of 6a,9a-difluoroprednisoione 17-butyrate in 2.5 cc of pyridine is treated with 1.25 cc of acetic anhydride and the reaction mixture permitted to stand overnight at 0°C. The reaction mixture is then poured into ice water and the crystaiiine precipitate formed is filtered off and recrystailized from a methylene chloride-ether-petroleum ether mixture to yield 494 mg of 6a,9a-difluoroprednisolone 17-butyrate, 21-acetate MP 191°-194°C. 

Esterification is normally carried out by treating the carbohydrate with an acid chloride or acid anhydride in the presence of a base (Sections 21.4 and 21.5). All the —OH groups react, including the anomeric one. For example, /3-o-glucopyranose is converted into its pentaacetate by treatment with acetic anhydride in pyridine solution. 

As previously discussed, solvents that dissolve cellulose by derivatization may be employed for further functionahzation, e.g., esterification. Thus, cellulose has been dissolved in paraformaldehyde/DMSO and esterified, e.g., by acetic, butyric, and phthalic anhydride, as well as by unsaturated methacrylic and maleic anhydride, in the presence of pyridine, or an acetate catalyst. DS values from 0.2 to 2.0 were obtained, being higher, 2.5 for cellulose acetate. H and NMR spectroscopy have indicated that the hydroxyl group of the methy-lol chains are preferably esterified with the anhydrides. Treatment of celliflose with this solvent system, at 90 °C, with methylene diacetate or ethylene diacetate, in the presence of potassium acetate, led to cellulose acetate with a DS of 1.5. Interestingly, the reaction with acetyl chloride or activated acid is less convenient DMAc or DMF can be substituted for DMSO [215-219]. In another set of experiments, polymer with high o -celliflose content was esterified with trimethylacetic anhydride, 1,2,4-benzenetricarboylic anhydride, trimellitic anhydride, phthalic anhydride, and a pyridine catalyst. The esters were isolated after 8h of reaction at 80-100°C, or Ih at room temperature (trimellitic anhydride). These are versatile compounds with interesting elastomeric and thermoplastic properties, and can be cast as films and membranes [220]. 

Esterification of tertiary alcohols poses several problems and expensive catalysts, like dimethylamino pyridine, are recommended. While esterification/transesterification/hydrolysis involving primary and secondary alcohols has been reported both with chemocatalysts and biocatalysts, terf-alcohol based esters have not found success. Recent work of Yeo et al. (1998) reports successful results for /er/-butyl octonoate using a new strain of lipase. This is a significant finding as the production of esters based on fert-alcohols (and reciprocally with hindered acids) may well be possible with biocatalysts, avoiding expensive catalysts and allowing easier separation. 

Substitution as a preceding reaction. In addition to the well known determination of primary and secondary alcohols via esterification with acetic anhydride in pyridine at about 98° C, esterification is possible at room temperature in ethyl acetate with perchloric acid117 or 2,4-dinitrobenzenesulphonic acid118 as a catalyst. However, as tertiary alcohols preferably split off their hydroxy group, they can be adequately determined by OH-substitution with HBr in glacial acetic acid according to... 

A further example is given in reference [88] Selective esterification of retronecine, the dialcoholic component of a pyrolizidine alkaloid, by the imidazolide method was found to be superior to the acid chloride/pyridine method. Acylation of the 9-position of retronecine with tiglic acid, pivalic acid, isobutyric acid, and propionic acid was investigated concerning the steric requirement of the carboxylic acid. 

The ratio of the a- to the j -anomeric D-glucosyl ester can be influenced by changing the reaction conditions. In DMF the a-anomer of the crocetin bis(D-glucosyl ester) was formed in about 70% yield.[196] Esterification of D-glucose with the imidazolides of benzoic acid or stearic acid in pyridine furnished a mixture of the a- and j -anomers of the C(l) glucosyl ester.[196]... 

The ability of a-hydroxyalkylphosphines with acceptor substituents to eliminate benzene on esterification with diphenylboric acid esters is so characteristic that it is impossible to obtain the intermediate esterification product even in the presence of pyridine. Instead of pyridinium dioxabora-taphosphoniarinane, the complex (110) of dioxaboraphosphorinane with pyridine was isolated [Eq. (66)] (86IZV643). 

The acetylation of amylopectin with pyridine and acetic anhydride presents more difficulty, even when using freeze-dried material,26 and the most satisfactory method is that involving prior dispersion in formamide, after which esterification occurs readily at room temperature. 

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