Acetic trialkyl

A Belgian patent (178) claims improved ethanol selectivity of over 62%, starting with methanol and synthesis gas and using a cobalt catalyst with a hahde promoter and a tertiary phosphine. At 195°C, and initial carbon monoxide pressure of 7.1 MPa (70 atm) and hydrogen pressure of 7.1 MPa, methanol conversions of 30% were indicated, but the selectivity for acetic acid and methyl acetate, usehil by-products from this reaction, was only 7%. Ruthenium and osmium catalysts (179,180) have also been employed for this reaction. The addition of a bicycHc trialkyl phosphine is claimed to increase methanol conversion from 24% to 89% (181). 

To return to a more historical development the mercuric acetate oxidation of substituted piperidines (77) should be discussed next. This study established that the normal order of hydrogen removal from the aW-carbon is tertiary —C—H > secondary —C—H > primary —C—H, an observation mentioned earlier in this section. The effect of substitution variations in the piperidine series can be summarized as follow s l-mcthyl-2,6-dialkyl and 1-methyl-2,2,6-trialkyl piperidines, as model systems, are oxidized to the corresponding enamines the 1,2-dialkyl and l-methyl-2,5-dialkyl piperidines are oxidized preferentially at the tertiary a-carbon the 1-methyl-2,3-dialkyl piperidines gave not only the enamines formed by oxidation at the tertiary a-carbon but also hydroxylated enamines as found for 1-methyl-decahydroquinoline (48) (62) l-methyl-2,2,6,6-tctraalkyl piperidines and piperidine are resistant to oxidation by aqueous mercuric acetate and... 

Monoalkylated and dialkylated acetic acids can be prepared by the malonic ester synthesis, but trialkylated acetic acids (R3CCO2H) can t be prepared. Explain. 

Two important classes of reactions use labelled tin compounds to prepare labelled compounds for mechanistic and analytical purposes. In the first type of reaction, labelled trialkyl- or triaryl tin hydrides (stannanes) are used to reduce (replace) several different groups such as halogen, —N02, —N=C, —N=C=Se, —COOR, —SR or an acetal group with a deuterium or a tritium atom. 

Preparation of 1-ethoxybenzylphosphonate — Reaction of a trialkyl phosphite with an acetal in the presence of boron trifluoride... 

Preparation of diethyl 3,5-di-t-butyl-4-hydroxybenzylphosphonate — Reaction of a benzylic acetate with a trialkyl phosphite... 

Additional advances have been made in the use of leaving groups other than halide for the nonphosphorus component of the Michaelis-Arbuzov reaction. The sensitive species 3,5-d i-t-b u ty I -4-hydroxybenzyl acetate has been noted to undergo efficient reaction (75-85% isolated yields) with a series of trialkyl phosphites upon heating at relatively low temperature (95°C) without the use of excess phosphite or additional catalyst.138 Chromatographic analysis of the reaction mixture indicates virtually quantitative conversion in the process. 

Mukmeneva, N.A., Cherezova, E.N., and Zhukova, R.S., Reactions of 3,5-di-terf-butyl-4-hydroxybenzyl acetate with trialkyl phosphites, Russ.. Gen. Chem., 64, 947, 1994. 

Typical electrophiles that attack olefins like Br+ (Eq. 64)105) and (OH)+ (Eq. 65) 105) do lead to electrophilic addition with ring enlargement101 a). Most interesting is the ability for electrophiles that normally do not attack olefins to also react. Thus, an oxycarbonium ion generated from an acetal smoothly alkylates the double bond of this composite functional group in an overall highly stereocontrolled 1,1,2-trialkylation of a simple ketone as illustrated in Eq. 66 106). The chemo- and... 

Heating of an allylic alcohol with an excess of trialkyl orthoacetate in the presence of trace amounts of a weak acid to give a mixed orthoester. The orthoester loses ethanol to generate the ketene acetal, which undergoes [3,3]-sigmatropic rearrangement to give a Y,5-unsaturated ester. 

Because carbohydrates are so frequently used as substrates in kinetic studies of enzymes and metabolic pathways, we refer the reader to the following topics in Ro-byt s excellent account of chemical reactions used to modify carbohydrates formation of carbohydrate esters, pp. 77-81 sulfonic acid esters, pp. 81-83 ethers [methyl, p. 83 trityl, pp. 83-84 benzyl, pp. 84-85 trialkyl silyl, p. 85] acetals and ketals, pp. 85-92 modifications at C-1 [reduction of aldehydes and ketones, pp. 92-93 reduction of thioacetals, p. 93 oxidation, pp. 93-94 chain elongation, pp. 94-98 chain length reduction, pp. 98-99 substitution at the reducing carbon atom, pp. 99-103 formation of gycosides, pp. 103-105 formation of glycosidic linkages between monosaccharide residues, 105-108] modifications at C-2, pp. 108-113 modifications at C-3, pp. 113-120 modifications at C-4, pp. 121-124 modifications at C-5, pp. 125-128 modifications at C-6 in hexopy-ranoses, pp. 128-134. 

Apart from 1,3,4-oxadiazole (b.p. 150°C), its lower alkyl derivatives and some dihydro compounds, 1,3,4-oxadiazoles are generally solids. In synthesis, the common method of purification is by crystallization of the crude reaction product. A few oxadiazoles, for example, alkyl ethers and acetates derived from 2,5-dihydro-2-hydroxy-2,5,5-trialkyl-l,3,4-oxadiazoles (cf. (38)), have been purified by distillation under reduced pressure. In some cases, chromatography over silica gel has been used. 

A one-pot procedure for the synthesis of 4-aminoquinazolines 771 from 2-aminobenzonitrile 770, ammonium acetate, and trialkyl orthoesters under solvent-free microwave conditions has been developed <2006JHC913>. Product yields are comparable to those obtained under thermal conditions, although reaction times are significantly shorter. An attempt to extend the method to include aromatic orthoesters was unsuccessful. 

Scheme 7.49). The requisite activated double bond is generated in situ from the 1,3-dicarbonyl compound and a one-carbon synthon such as a trialkyl orthoformate, diethoxymethyl acetate or Al,Al-dimethylformamide dimethyl acetal. 

The earlier work on chloroacetone (18,19) already indicated that trialkyl amines were superior to other bases for this reaction. Therefore the decision to use trialkyl amines to scavenge HCl was already determined by the literature precedent. However, when compared to the tributyl amine, smaller amines might be preferred since they could boost the reactor productivity by reducing the volume. Unfortunately, for unknown reasons, the process did not work as well with the simpler amines. Both tripropyl amine and triethyl amine displayed both lower rates and lower selectivity for methyl pivaloyl acetate. (See Table 6.)... 

Preparation of peroxy ortho esters by the reaction of trialkyl orthoformates, orthoacetates, orthobenzoates, ketene acetals, and 2-phenyl-2-methoxy-l,3-dioxolanes with hydroperoxides or oxygen [194-197]. 

Mannitol hexanitrate is obtained by nitration of mannitol with mixed nitric and sulfuric acids. Similarly, nitration of sorbitol using mixed acid produces the hexanitrate when the reaction is conducted at 0—3°C and at —10 to —75°C, the main product is sorbitol pentanitrate (117). Xylitol, ribitol, and L-arabinitol are converted to the pentanitrates by fuming nitric acid and acetic anhydride (118). Phosphate esters of sugar alcohols are obtained by the action of phosphorus oxychloride (119) and by alcoholysis of organic phosphates (120). The 1,6-dibenzene sulfonate of D-mannitol is obtained by the action of benzene sulfonyl chloride in pyridine at 0°C (121). To obtain 1,6-dimethanesulfonyl-D-mannitol free from anhydrides and other by-products, after similar sulfonation with methane sulfonyl chloride and pyridine the remaining hydroxyl groups are acetylated with acetic anhydride and the insoluble acetyl derivative is separated, followed by deacetylation with hydrogen chloride in methanol (122). Alkyl sulfate esters of polyhydric alcohols result from the action of sulfur trioxide—trialkyl phosphates as in the reaction of sorbitol at 34—40°C with sulfur trioxide—triethyl phosphate to form sorbitol hexa(ethylsulfate) (123). 

Selectivity can be an overriding commodity in cases where reactivity is dictated by logic and accepted concepts. Such is the case with stannylene acetals of diols and trialkyl-stannyl ethers of alcohols. Enhanced nucleophilicity of oxygen attached to tin and well-documented stereoelectrorric effects associated with methine carbon atoms of trialkyhin ethers lead to remarkably selective reactions of (7-substitution and oxidation in polyhydroxy compounds. 

Figure 1. Influence of chain length of trialkyl-substituted germanium, tin, and lead acetates on minimum concentration inhibitory to Aspergillus niger.------, germanium - tin --------, lead.

The second approach for the nucleophilic animation reactions to be considered here will be reactions of allyl halides and allyl acetates leading to allyl amines. Allyl halides are normally very reactive in SN2 reactions, but the direct coupling of allyl halides with nitrogen nucleophiles has been performed with limited success [4], as di- and trialkylated by products often predominate. The application of the Gabriel synthesis can to a certain extent eliminate the problem with polyalkylation of amines using, e.g., the stabilized phthalimide anion 19 as the nucleophile. The allyl amine 20... 

Yamamoto et al. reported full research details on catalytic enantioselective protonation under acidic conditions in which prochiral trialkylsilyl enol ethers and ketene bis(trialkyl)silyl acetals were protonated by a catalytic amount of Lewis acid assisted Bronsted acid (LBA15 or 16) and a stoichiometric amount of 2,6-dimethylphenol as an achiral proton source [20]. 

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