Acetates and Benzoates

TMq layers of silicic acid containing 10% starch binder [53], silica gel G [19, 54, 55], and Magnesol (Firm 150) containing calcium sulfate (13%) [56] give good resolutions. Magnesol must be washed thoroughly with dilute acetic acid before use to avoid deacylation catalyzed by traces of alkali. 

Benzene and mixtures of benzene with methanol or ethyl acetate resolve the acylated sugars with the acetates requiring more polar solvents than the benzoates. The hRf values of some peracetylated sugars are given in Table 208. 

Two phase paper chromatography with dimethyl sulfoxide (DMSO) as the stationary phase was used successfully by Wickberg [59] for 

17 Standard dyes (Sudan III, methyl red, methyl orange) 

D-glycero-D-galacto-Heptose hexabenzoate D-Glucopyranose pentaacetate 26 0 XXIX 

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The irradiation of the provitamin has been achieved using the acetate and benzoate esters, although the free alcohol form of the provitamin is usually used (77). 

FeCl3, CH2CI2, 2-3 min, 68% yield. Benzyl ethers are cleaved in 15-20 min under these conditions. Methyl glycosides, acetates and benzoates were not affected by this reagent. 

The complete conversion of an alcohol to products is only possible if the decomposition of the lead IV alkoxide is much faster than decomposition of lead IV acylate. This is only true for the acetate and benzoate, less for the propionate and not at all for lead IV iso-butyrate ... 

AC2O or AcCl, Pyr, DMAP, 24-80°, 1-40 h, 72-95% yield. The use of DMAP increases the rate of acylation by a factor of lO. These conditions acylate most alcohols, including tertiary alcohols. The use of DMAP (4-A,A-dimethylaminopyridine) as a catalyst to improve the rate of esterification is quite general and works for other esters as well, but it is not effective with hindered anhydrides such as pivaloic anhydride. The phosphine i (48-99% yield) and Bu3P have been developed as active acylation catalysts for acetates and benzoates. 

This is an Sn2 process, since inversion is found at R. Another good leaving group is NTS2 ditosylamines react quite well with acetate ion in dipolar aprotic solvents RNTs2 4- OAc — ROAc. Ordinary primary amines have been converted to acetates and benzoates by the Katritzky pyrylium-pyridinium method (p. 447). Quaternary ammonium salts can be cleaved by heating with AcO in an aprotic solvent. Oxonium ions can also be used as substrates RsO -f R COO —> R COOR R2O. 

At first we determined, by means of the DVP method, ifTMAX of 2,4-dinitro-phenolate, 2,5-dinitrophenol picrate, acetate and benzoate, which lay between 10 3 and 10 5. Next, separate potentiometric titrations of 2,5-dinitrophenol and picric acid were carried out on the basis of the previously known (see above) ptfax = 6.5 and P hx2- = 100 for 2,5-dinitrophenol and p.fiTHX = 3.0 for picric acid, we calculated titration curves for estimated values of 0 and obtained, for the best fit between the experimental and calculated curves, K o = 10 21 for both 2,5-dinitrophenol and picric acid. In both instances changing fTMA0H for 1 to 10 6 did not alter the calculated titration curve. Finally, for potentiometric titrations of other acids with TMAOH while using / TMAX values from DVP results, in addition to Kn 0 = 10 21, we obtained the best fit between the experimental and calculated curves again when pifbenzoic acid = 1 (see Fig. 4.12)... 

Cleavage of benzyl ethers3 Anhydrous FeCl3 in CH2C12 cleaves carbohydrate benzyl and p-phenylbenzyl ethers at 25° without effect on methyl ethers or acetate and benzoate groups. Yields are usually >70%. 

Apart from glycosyl acetate and benzoate donors, more elaborate O-carbonyl derivatives offer potential for distinct modes of anomeric leaving group activation. Many of these donors (Scheme 3.21) involve activation of an anomeric O-carbonyl derivative 134 at a remote functional group (Y). The adivated remote functionality, in turn,... 

The acyl moiety can be aliphatic or aromatic, as has been shown with several acetates and benzoates. 

The chemistry of manganese(III) with monodentate carboxylates, such as acetate and benzoate or their derivatives, results in the formation of complexes with nuclearities of 2, 3, 4, 6, 7, 8, 9, 10, and 18. The chemistry of polynuclear carboxylate complexes is too extensive to detail here and coverage is confined to a brief discussion of the structural types involved. 

Protection of an alcohol function by esterification sometimes offers advantages over use of acetal or ether groups. Generally, ester groups are stable under acidic conditions. Esters are especially useful in protection during oxidations. Acetates and benzoates are the most commonly used ester derivatives. They can be conveniently prepared by reaction of unhindered alcohols with acetic anhydride or benzoyl chloride, respectively, in the presence of pyridine or other tertiary amines. 4-Dimethylaminopyridine (DMAP) is often used as a catalyst. The use of A-acylimidazolides (see Section 3.4.1) allows the... 

Mohammadpoor-Baltork I, Khosropour AR (2002) Efficient and selective conversion of trimethylsilyl and tetrahydropyranyl ethers to their corresponding acetates and benzoates catalyzed by bismuth(III) salts. Monatsh Chem 133 189-193... 

Cinnamic acid is decomposed, like the acids of the amylio series, when treated with fused potassio hydrate it gives, under these circumstances, potassic acetate and benzoate. For the analogous reaction in the acrylic series see p. Sid. 

Tetrahedral tetraazonium compounds 5a and 5b, developed by Schmidt-chen, bind carboxylates, such as formiate, acetate, and benzoate, among a variety of other anions [8]. Although these receptors do not display hydrogen bond interactions, they are endowed with well localized polycationic centers, which are independent on the acidity of the medium. A ditopic receptor build up of both a 5a and a 5b subunits bridged by a p-xylylene spacer showed selectivity towards the largest members of a series of dianionic probes [9],... 

Acetates and benzoates are widely used as characteristic derivatives of carbohydrates, and for the assay and protection of hydroxyl groups. Various maltose heptaacetates having a free hydroxyl group on C-l, C-2, C-3, C-6, or C-6 have been synthesized. 2,3,6,2, 3, 4, 6 -Hepta-0-acetyl-/3-maltose (17) has been prepared by hydrolysis of the corresponding glycosyl halide.57,58 The reaction conditions may not always result in the isolation of the anomerically unsubstituted acetate, as was shown by Corbett and coworkers,59 who obtained three... 

In 1963, a series of systematic studies was begun on the reaction of fully acylated disaccharides (acetates and benzoates) with methanolic or aqueous solutions of ammonia at room temperature. Octa-O-acetyl-a-cellobiose in 16% methanolic ammonia afforded44 1,1-bis-(acetamido)-l-deoxycellobiitol (45) and N-acetyl-a-cellobiosylamine (46), which is the anomer of the cellobiosylamine previously described by Zechmeister and Toth41 and Micheel and coworkers.43... 

As previously indicated (see pp. 88-91), formation of heterocyclic compounds, mainly pyrazines, was found only in the ammonolysis of some aldose nicotinates33 35 and acetates and benzoates of ketoses.39 37 For ketose esters, whose behavior differed from that of the aldose esters, the formation of imidazole derivatives was also observed these heterocyclic compounds also result from the direct action of ammonia upon the corresponding free sugars, but the presence of the esterifying acyl groups evidently increases their ease of formation and raises their yields. 

All-carbon ene reactions can go in reverse when ring-strain is released 6.24. This reaction is curious, because it could also be considered as a homologue of a [1,53-sigmatropic rearrangement—it is quite common to think of the chemistry of cyclopropanes as similar to that of alkenes. With heteroatoms in the chain it is possible to drive such reactions in reverse without having to release strain. Thus esters such as acetates and benzoates undergo a cyclic (3-elimination on pyrolysis. This type of elimination is known to be syn... 

It appears that the initial lack of interest in sulfonic esters of carbohydrates can be attributed to the fact that sugar chemists were so accustomed to thinking of sugar esters in terms of carboxylic esters (particularly, acetates and benzoates) that they overlooked an earlier... 

Typical OH-scavengers suppress this reaction of (OP)2Cu+ (Que et al. 1980) yet, acetate and benzoate seem to be equally efficient, despite the fact that acetate is nearly two orders of magnitude less reactive towards OH than benzoate (k=7 X 107 dm3 mol-1 s 1 vs k = 5 X 109 dm3 mol-1 s 1 Buxton et al. 1988), and obviously it is not a freely diffusing OH that is responsible for the reaction. The reaction is also suppressed by Cu-complexing compounds and by transition metal ions such as Zn2+, Co2+, Cd2+ and Ni2+ that form stable complexes with 1,10-phenanthroline (Que et al. 1980) and also by competitive intercalators such as ethidium bromide and 2,9-dimethyl-l,10-phenanthroline (Reich et al. 1981). Interestingly, compared to its parent, the latter is inactive. NADH may serve as a reductant, but 02, seems to be a salient intermediate in this cleavage reaction, because cleavage is fully suppressed in the presence of SOD (Reich et al. 1981). 

The esters, 7-ethoxycyclopropyl acetate (7 a) and benzoate (7b) have been synthesized by the addition of the Simmons-Smith reagent 22> to 1-ethoxy vinyl acetate and benzoate, respectively.4) A potential difficulty in this reaction lies in the fact that zinc iodide, a Lewis acid, is generated in the process and may induce cyclopropane ring opening (Section 4.3.3). However, when glyme is used as a solvent, the acid-labile bonds remain intact since the zinc salt is insoluble in this medium.23)... 

Molecules 20-22 in which a ferrocene-lj -bisamide is bridged across the upper rim of a calix[4]arene show interesting anion sensing selectivity [19]. The results of H NMR studies in CD3CN show that the receptors preferentially bind carboxylate anions (acetate and benzoate) over dihydrogenphosphate and chloride. 

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