Alkanols, esterification

XRD samples 638 f alignment defects, displays 756 alignment materials, displays 732 aliphatic chains 125,395 alkanes, solvents 883 alkanoic acids, esterification alkanols, esterification 106 alkenes, solvents 883 alkenyl, terminal substituents alkyl functionalization, arenes alkyl groups... 

Amino alcohols can be resolved by a number of pathways including hydrolysis, esterification, and transesterification. For example, hydrolysis of Ai,0-diacet5l-2-amino-l-butanol with PPL followed by recrystallization results in (80a) with 95% ee (108). Hydrolysis of racemic acetates or butyrates of 2-[(aLkoxycarbonyl)amino]-l-aLkanols with PFL gives (R)-alcohol (81) with 95% ee (109). (3)-(81) can be obtained by transesterification of the racemic (81) with ethyl acetate which also serves as the reaction medium (109). 

Polynitroaliphatic alcohols containing nitro groups on the carbon fi to the hydroxy functionality are less basic than their alkyl counterparts. This decreased basicity of the hydroxy group makes reactions such as esterification, acetal formation and alkylation much slower than usual, and in some cases, these reactions may not proceed without catalysts. To add to the problem, normal base catalysts cannot be used in conjunction with 2,2-dinitroalkanols and l,l,l-trinitro-2-alkanols because of their facile dissociation in alkaline solution. 

Enantioselective enzymatic esterifications of trimethylsilyl-substituted alcohols with racemic 2-(4-chlorophenoxy)propanoic acid in water-saturated benzene, catalyzed by the Candida cylindracea lipase OF 360 CCL OF 360 E.C. 3.1.1.3) have been used to prepare (—)-2-(4-chlorophenoxy)propanoic acid76,77. As shown in Scheme 23, the (trimethylsilyl)alkanols 95, 97 and 99 were converted enantioselectively into the corresponding (trimethylsilyl)alkyl (+)-2-(4-chlorophenoxy)propanoates 96, 98 and 100. The enantiomeric purity of the remaining (—)-2-(4-chlorophenoxy)propanoic acid was 95.8% ee (95), 76.1% ee (97) and 77.5% ee (99). 

Fischer-Speier esterification to give a salt of an amino acid ester (by refluxing an alkanol with anhydrous HC1 or hot benzyl alcohol with toluene-/>-sulphonic acid) is straightforward. The fact that the nearby amino group is protonated when the carboxy group reacts to give a-amino acid esters does not slow the reaction down unduly a nearby positive site might have been expected to reduce the electrophilic character of the carboxy carbon atom. Without an acid catalyst, Walkylation can accompany esterification (Equation 4.6). 

Both enantiomers of lactic acid (2-hydroxypropanoic acid) are natural products and easily obtained by biotechnological methods, so there is no need for their synthesis in the laboratory. Even their esters with alkanols, e.g.. 1, are comparatively inexpensive and, therefore, convenient starting materials for derivatization to chiral reagents and auxiliaries. If necessary, such esters can be obtained by any convenient esterification technique. O-Acylated derivatives of lactic esters have been used very successfully as chiral auxiliaries in diastereoselective Diels-Alder reactions (Section D.1.6.1.1.1.1.2.). The acrylate 2 and methacrylate 31-3 and the fu-marate 43 give very high enantiomeric excesses. These are obtained from the lactic ester by treatment with an acid chloride. 

The esterification of carboxylic acids can also be accomplished using synthetic equivalents of acetals of alkanols RCH(OR )2 (by acid catalysis), ortho-esters RC(0R )3 (by acid catalysis), and dialkylcarbonates C0(0R)2 (by base catalysis). A series of bifunctional reagents of this type—dimethylformamide dialkylacetals (CH3)2N-CH(0R )2—are available at present. These compounds also react with primary amino groups, that is used in derivatization of amino acids for GC analysis (Fig. 1). 

Esters are generally prepared by reaction of an acid with an alcohol. In the presence of a catalyst the raw materials are heated to temperatures up to 250 °C to remove water and to obtain high conversion. Due to the thermal instability of quaternary ammonium compounds, they are not recommended for use with alcohol or acid functions in the esterification. In the case of esteramines, the esterification is usually carried out with tertiary alkanol-amines and fatty acids. The corresponding esteramine is reacted with an alkylating agent like dimethyl sulfate or methyl chloride to obtain the corresponding quaternary ammonium compound. 

Yoshino et al. [146,147] esterified a fluorinated alkanol, such as IH, H, 9//-hexadecafluorononanol-l, with maleic anhydride in the presence of p-tolue-nesulfonic acid monohydrate. The resulting bis-maleate ester reacted with sodium hydrogen sulfite to yield the sodium salt of the fluoroalkyl-2-sulfosuccinate. Oxyethylene groups were introduced by reacting the corresponding fluorinated alcohols with ethylene carbonate prior to esterification with maleic anhydride [148]. 

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