Tartarate ester

As a general guide, however, it may be noted that the following have fairly easily recognisable odours methyl and ethyl formate methyl and ethyl acetate (apples) methyl and ethyl benzoate methyl salicylate (oil of winter-green) and ethyl salicylate methyl and ethyl cinnamate. (It is however usually impracticable to distinguish by odour alone between the methyl and ethyl esters of a particular acid.) Methyl and ethyl o. alate, and methyl and ethyl phthalate are almost odourless. Succinic and tartaric esters have faint odours. 

The first practical method for asymmetric epoxidation of primary and secondary allylic alcohols was developed by K.B. Sharpless in 1980 (T. Katsuki, 1980 K.B. Sharpless, 1983 A, B, 1986 see also D. Hoppe, 1982). Tartaric esters, e.g., DET and DIPT" ( = diethyl and diisopropyl ( + )- or (— )-tartrates), are applied as chiral auxiliaries, titanium tetrakis(2-pro-panolate) as a catalyst and tert-butyl hydroperoxide (= TBHP, Bu OOH) as the oxidant. If the reaction mixture is kept absolutely dry, catalytic amounts of the dialkyl tartrate-titanium(IV) complex are suflicient, which largely facilitates work-up procedures (Y. Gao, 1987). Depending on the tartrate enantiomer used, either one of the 2,3-epoxy alcohols may be obtained with high enantioselectivity. The titanium probably binds to the diol grouping of one tartrate molecule and to the hydroxy groups of the bulky hydroperoxide and of the allylic alcohol... 

Only reaction 1 provides a direct pathway to this chiral molecule the intermediate 2-methyl-butanal may be silylated and reacted with formaldehyde in the presence of the boronated tartaric ester described on page 61. The enantiomeric excess may, however, be low. 

The enantioselective epoxidation method developed by Sharpless and co-workers is an important asymmetric transformation known today. This method involves the epoxidation of allylic alcohols with fcrt-butyl hydroperoxide and titanium (sopropoxide in the presence of optically active pure tartarate esters, see Eqn. (25). 

Two types of these emulsifiers are calcium and sodium stearoyl lactylates (CSL, SSL) and diacetyl tartaric esters of mono and diglycerides (DATEM esters). The bread and flour regulations 1984 permit the use of SSL at up to 5 g kg-1 in all bread while DATEM esters are permitted in all bread without limit. Typical use levels are around 0.5% on flour weight. CSL and SSL have been permitted in the USA since 1961. 

Dimerisation and ester coordination restricts the number of sites available for alkoxides to two only, while maintaining a comparatively Lewis-acidic titanium centre, as needed for the reaction. In the dimer, the methine protons, alkoxide groups, and ester groups are inequivalent, but they show a rapid exchange on the H NMR timescale at room temperature, as the AG for the process is only 64 kl.mol. This process is much faster than the catalytic reaction, but due to the C2-symmetry of the tartaric esters the resulting structures of the dimers are the same. 

Although it was also Henbest who reported as early as 1965 the first asymmetric epoxidation by using a chiral peracid, without doubt, one of the methods of enantioselective synthesis most frequently used in the past few years has been the "asymmetric epoxidation" reported in 1980 by K.B. Sharpless [3] which meets almost all the requirements for being an "ideal" reaction. That is to say, complete stereofacial selectivities are achieved under catalytic conditions and working at the multigram scale. The method, which is summarised in Fig. 10.1, involves the titanium (IV)-catalysed epoxidation of allylic alcohols in the presence of tartaric esters as chiral ligands. The reagents for this asyimnetric epoxidation of primary allylic alcohols are L-(+)- or D-(-)-diethyl (DET) or diisopropyl (DIPT) tartrate,27 titanium tetraisopropoxide and water free solutions of fert-butyl hydroperoxide. The natural and unnatural diethyl tartrates, as well as titanium tetraisopropoxide are commercially available, and the required water-free solution of tert-bnty hydroperoxide is easily prepared from the commercially available isooctane solutions. 

Sharpless Asymmetric Epoxidation This is a method of converting allylic alcohols to chiral epoxy alcohols with very high enantioselectivity (i.e., with preference for one enantiomer rather than formation of racemic mixture). It involves treating the allylic alcohol with tert-butyl hydroperoxide, titanium(IV) tetra isopropoxide [Ti(0—/Pr)4] and a specific stereoisomer of tartaric ester. For example,... 

Table 12. CH-CH Shifts and Coupling Constants of the Tartaric Ester Moiety of 0,0 -Diacyltartaric Acid Esters of ac-Amino Alcohols with Rigid Ring Structure (d, DMSO-rf6)...

Traditionally, large oak barrels are used to facilitate the diffusion of oxygen. This is assumed to play a major role in the many chemical reactions occurring during aging. Oxidation reactions promote desired changes in wine phenolics (e.g., anthocyanins, flavonoids, and tartaric esters of hydrocinnamic acids) as well as oak phenolics extracted from the... 

The chiral precatalyst is a titanium species. It is generated by the in situ treatment of titanium isopropoxide with diethyl or diisopropyl tartarate. The relative amounts of Ti(OPr )4 and the tartarate ester have a major influence on the rate of epoxidation and enentioselectivity. This is because the reaction between Ti(OPr )4 and the tartarate ester leads to the formation of many complexes with different Ti tartarate ratios. All these complexes have different catalytic activities and enantioselectivities. At the optimum Ti tartarate ratio (1 1.2) complex 9.35 is the predominant species in solution. This gives the catalytic system of highest activity and enantioselectivity. The general phenomenon of rate enhancement due to coordination by a specific ligand, with a specific metal-to-ligand stoichiometry, is called ligand-accelerated catalysis. 

Among the hydroxycinnamic acids, caftaric acid predominates (up to 50% of total hydroxycinnamic acids). Other important substances are the tartaric esters of p-coumaric acid and ferulic acid, and the franx-p-coumaric glucoside (Somers et al. 1987). The concentration levels of hydroxycinnamic acid derivatives in wine depend on many factors like grape variety, growing conditions, climate, etc. It is... 

In grapes or grape juices, the tartaric esters may be hydrolysed by enzymes from contaminant fungi or from commercial pectolytic preparations, both with cin-namoyl decarboxilase activity, releasing free hydroxycinnamic acid forms (Dugelay et al. 1993 Gerbaux et al. 2002). However, the tartaric esters are mostly hydrolysed after malolactic fermentation (Hernandez et al. 2006, 2007), it being hypothesised that the hydrolytic activity of lactic acid bacteria follows the completion of malic conversion to lactic acid (Cabrita et al. 2007) (see Table 11.4). 

Before the turn of the century, Maquenne had prepared imidazole-4,5-dicarboxylates from tartaric ester dinitrates with either an aliphatic aldehyde or precursor in the presence of ammonium ions at pH values 3.5-6.S. Hydrolysis, especially with bromoacetic acid, of the resulting dicarboxylate esters gives imidazole-4,5-dicarboxylic acid (Scheme 75) <70AHC(12)103). 

The use of alkyUiydroperoxides as epoxidizing agents for allylic alcohols under catalytic conditions was soon expanded into enantioselective epoxidation with use of the more mild titanium alkoxides in the presence of chiral tartaric esters. As concerns the epoxidation of functionalized dienes, these now so-called Sharpless conditions [Ti(OPP)4, diaUtyl tartrate, TBHP] have been utilized to enantioselectively epoxidize 1,4-pentadiene-... 

Diethyl tartrate, the allylic alcohol, and the oxidant r-BuOOH displace the iso-propoxide groups on titanium to form the active Ti-catalyst in a complex ligand exchange pathway. From structural and kinetic studies, " Sharpless proposed that oxygen transfer occurs from a dimeric complex that has one tartaric ester moiety per titanium atom. 

The absolute configuration of the epoxy alcohol is predictable using the mnemonic model depicted below in which the CH2OH group is positioned at the lower right. As a rule, the transfer of the epoxide oxygen occurs from the upper face of the allyl alcohol when (- -)-(/ , / )-tartaric esters are used, while the lower face is attacked when the (-)-(5, 5)-tartrates are used. " ... 

PGE Polyglycerol Esters of fatty acids DATEM Diacetyl Tartaric Esters of Mono-digiycerides GLP Glycerol Lacto Palmitate (Lactic acid esters)... 

Asymmetric 1,3-dipolar cycloaddition of nitrile oxides to allyl alcohol has been performed by Ukaji and coworkers [1542] in the presence of Et2Zn and (/V )-tartaric esters 2.69 in stoichiometric amounts at 0°C. Diisopropyl tartrate gjves the best results, and 2-isoxazolines are obtained with an excellent enantiose-lectivity (Figure 9.11). 

Datagel. [Croda Chem. Ltd.] Diacetyl tartaric ester monoglyceride food emulsifier. 

Datamuls . [Goldschmidt AG) Diacetyl tartaric ester monoglyceride fo< emulsifier. 

This means that this substituent has to be arranged by a kinetically controlled stereo selective method, which in our case was a Hetero-Diels Alder reaction between a diene 164 and a glyoxylate 165. Ketone 166 is the precursor of 164 and tartaric ester 167 that of 165. The methyl ether 164 could not been made by deprotona-tion/methylation of 166 (Scheme 27). 

Tartaric acid, however, can be converted into glyoxylic acid only by periodic acid since lead tetraacetate attacks all four carbon atoms of tartaric acid.146 Weygand nevertheless worked out a method of obtaining glyoxylic esters from tartaric esters by means of lead tetraacetate because hydroxy esters are as resistant to cleavage as are esterified or etherified glycols. 

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