Alkyl Acetates Research Articles

Thermolytic reactions of esters. Part XIII The effect of electron‐attracting α‐substituents in alkyl acetates

Abstractα‐Alkylation of esters, e.g. AcO‐iPr → AcO‐tBu, results in a large rate increase for β‐elimination of acetic acid, indicating that in the transition state Cα is positively charged. Replacement of α‐H by electron‐attracting groups Z, such as COOMe, also enhances the rate of formation of alkene. Neither differences in product stability nor steric acceleration appear to play a significant role. A major factor is dipolar destabilization of starting compounds containing two electronegative groups, such as AcOCMe2Z compared with AcO‐tBu. The free energies of the transition states are found to parallel those of the fully ionized species, AcO(‐) + R(+).At elevated temperatures, esters such as AcOCMe(CN)Ph will give rise to O‐C bond homolysis rather than to molecular elimination of acetic acid.

Thermolytic reactions of esters. Part 12. Steric versus polar effects in pyrolytic β-elimination of acetic acid from (tertiary) alkyl acetates

The vapour-phase pyrolysis of the crowded tertiary alkyl acetates AcOCMe2But(II) and AcOCMePri2(III) to give acetic acid and the appropriate alkene(s) has been studied. Rates of formation of alk-1-ene and of isobutene from t-butyl acetate were compared. On this basis steric acceleration in pyrolysis of AcOR, employing known steric parameters E′s from groups R, is quantitatively analysed. Although the steric effect can be quite substantial, the remarkable rate increase in the series AcOEt–AcOPri–AcOBut is largely due to a polar effect. A rationale is presented for the apparent inconsistency: the rate effect of α-alkylation in R is even larger than that in SN1-type solvolysis of RBr, suggesting a large charge separation AcO–, R+ in the transition state for concerted β-elimination, whereas the Hammett ρ value observed for pyrolysis of e.g. AcOCH(Me)C6H4Z is only a few percent of that associated with formation of benzylic carbenium ions.

Chlorination of Carboxylic Acid Derivatives. IX. Liquid Phase Chlorination of Aliphatic C2--C8 Alkyl Acetates. EI Mass Spectra of Monochlorinated Esters.

Chlorination of Carboxylic Acid Derivatives. IX. Liquid Phase Chlorination of Aliphatic C2--C8 Alkyl Acetates. EI Mass Spectra of Monochlorinated Esters.

The mechanism of thermal elimination. Part 17. Rate data for pyrolysis of vinyl acetate and 1,2-diacetoxyethane

Between 721.7 and 636.4 K, vinyl acetate undergoes thermal decomposition according to the rate equation log (k/s–1)= 10.43 – 182.4/2.303 RT(R= 8.312 J mol–1 K–1). Approximately 95% of reaction is decarbonylation to give acetone, with decomposition to ketene and acetaldehyde being the minor component. The latter reaction is an analogue of acetic anhydride pyrolysis which takes place at least 106 times faster per β-hydrogen at 600 K. This very large rate difference parallels that between β-keto-acids and βγ-alkenoic acids and contrasts markedly with pyrolysis of alkyl acetates and alkyl vinyl ethers, which occurs at closely similar rates. The contrasting behaviour most probably reflects differences in the principal bond-breaking step of the reaction, which for vinyl acetate and acetic anhydride (and also the acids) is breaking of the β–X–H bond so that the nucleophilicity of the attacking group assumes major importance; for esters and vinyl ethers this is not the most important step so their reaction rates are similar. The relative reactivities to the acids support an alternative view that both vinyl acetate and acetic anhydride pyrolyse via their enol forms. The greater understanding of the factors affecting gas-phase elimination rates permits prediction of the relative rates of compounds not yet studied. Pyrolysis of 1,2-diacetoxyethane gave non-first-order plots, with rate acceleration due to formation of the more reactive vinyl acetate. The β-acetoxy-group (OCOMe) increased the rate of elimination (per β-hydrogen at 600 K)ca. 7-fold, which compares with factors of 388 and 144 for COMe and CO2Me respectively, and a reduction of 3.6-fold by OMe.

Gas chromatography of homologous esters : XX. Capillary column studies of alkyl acetates, chloroacetates, dichloroacetates and trichloroacetates

Isothermal capillary gas chromatography of C 1-C 8 n-alkyl acetates, chloroacetates, dichloroacetates and trichloroacetates has been studied using a low-polarity (SE-30) and a polar (OV-351) stationary phase at increasing temperatures from 100 to 160°C. The work extends recent studies of Komarek and co-workers and shows the effect of retention index increments on the methylene chain and of the various chlorine substituents in the individual homologous series.

Gas-liquid chromatographic analyses: VII. Gas chromatography of C1—C8n-alkyl acetates and methyl esters of aliphatic C2—C9n-carboxylic acids and certain of their monochlorinated derivatives on carbowax 20M and SE-30 glass capillary columns

The gas chromatography of mixtures of n-alkyl acetates (CH3COOR, R = C1—C8) and methyl esters of aliphatic n-carboxylic acids (R′COOCH3, R′ = C1—C8) and certain of their monochlorinated derivatives has been studied on Carbowax 20M and SE-30 glass capillary columns under the same operating conditions. The separation of the isomeric monochlorinated esters was complete on Carbowax 20M, whereas on SE-30 the peaks of 6- and 7-chlorooctyl acetates and methyl (ω − 1)- and (ω − 2)-chlorooctanoates and -nonanoates partly overlapped. The complete separation of the mixtures could not be achieved, however, on Carbowax 20M, in spite of the use of various operating conditions. The results show that all 44 individual components can be separated using columns with polar and non-polar stationary phases. The relative retention times for the compounds are given and the elution order is discussed. The retention times of alkyl acetates are always shorter that those of methyl esters with the same chain lengths (RR′). The greatest disparities are observed between the retention behaviours of 1-chloroalkyl acetates and methyl 2-chloro esters, whereas the effect fo a chlorine substituent further away seems to be negligible.

ChemInform Abstract: 1,3‐O‐ to ‐C‐Alkyl Migration of 1‐Alkenyl Alkyl Acetals and Ketals Catalyzed by Boron Trifluoride. Selective Cross‐ and Regioselective Aldol Type Reactions.

AbstractKetale wie (I), die man durch Addition von Allylalkoholen an Vinylether erhält, werden mit Bortrifluorid in Keto‐ether wie (III) umgelagert.

ChemInform Abstract: 1,3‐O‐ to C‐Alkyl Migration of 1‐Alkenyl Alkyl Acetals Catalyzed by Boron Trifluoride. A Novel Cross Aldol Type Reaction.

AbstractDie aus Alkenylethern (I) und Allylalkoholen (II) in Gegenwart von Pyridinium‐p‐toluolsulfonat hergestellten Allylacetale (III) reagieren in Gegenwart eines Rutheniumtriphenylphosphin‐Katalysators unter Doppelbindungsverschiebung zu Enolacetalen (IV).

ChemInform Abstract: Alkyl Acetates by Stoichiometric Reaction of Alcohols with the Methylene Bridged Complex [Fe2( n‐CH2)(CO)8

AbstractDie stöchiometrische Reaktion des methylenverbrückten Eisenkomplexes (I) mit Methanol oder Ethanol (II) führt zu den Estern (III).

Lewis Acid Induced α‐Alkylation of Carbonyl Compounds

AbstractCarbonyl compounds undergo α‐alkylation via the corresponding silyl enol ethers using SN1 active alkyl halides or acetates in the presence of Lewis acids. This methodology extends the scope of carbonyl chemistry considerably, since SN1 active alkylating agents are generally base sensitive and therefore unsuitable for reactions with enolate anions or nitrogen analogs. A prime example is the α‐tert‐alkylation of aldehydes, ketones and esters.

Diastereoselection in 1,3-O- to -C-alkyl migration reaction of 1-alkenyl alkyl acetals catalyzed by boron trifluoride etherate

Remarkable diastereoselection, with (E)-alkenyl alkyl acetal giving selectively the erythro α-alkyl-β-alkoxyaldehyde, and (Z)-acetal leading preferentially to the threo isomer, is observed in the 1,3-O- to - C-alkyl migration reaction of 1-alkenyl alkyl acetals catalyzed by boron trifluoride etherate.

1,3-O- to -C-alkyl migration of 1-alkenyl alkyl acetals and ketals catalyzed by boron trifluoride. Selective cross- and regioselective aldol type reactions

1,3-Alkyl migration of 1-alkenyl alkyl acetals and ketals is effectively catalyzed by trifluoroborane etherate to give cross aldol type products selectively. Remarkable regio-selectivity is observed in the synthesis of α-alkyl-β-alkoxy-ketones.

Esters of α-arylalkanoic acids from ‘masked’α-halogenoalkyl aryl ketones and silver salts: synthetic, kinetic, and mechanistic aspects

A method for the synthesis of alkyl esters of α-arylalkanoic acids is given, based on silver-ion-assisted (AgBF4, AgOSO2CF3, AgSbF6, AgNO3) solvolysis of alkyl acetals of primary and secondary α-halogenoalkyl aryl ketones (Hal = I, Br, Cl) in an alcoholic medium (methanol, ethanol). The reaction is quite selective and alkyl esters are the only reaction products; ethers, which are possible substitution products, are not found. The importance of masking the carbonyl as the acetal is emphasised. The reaction is found to be first-order in AgBF4 and in the primary α-halogeno acetal. A three-point Hammett correlation (ρ=–3.29) between σ+ and the rate constants suggests a large cationic contribution as well as strong aryl participation in the transition state.The role played by the oxygen of the acetal group in the specificity of the reaction is discussed in comparison with the reactivity of analogous compounds with saturated skeletons and of α-halogenoalkyl aryl ketones.

1,3-O- TO C-ALKYL MIGRATION OF 1-ALKENYL ALKYL ACETALS CATALYZED BY BORON TRIFLUORIDE. A NOVEL CROSS ALDOL TYPE REACTION

Abstract 1,3-O- to C-alkyl migration of acyclic 1-alkenyl alkyl acetals catalyzed by BF3·Et2O gives selectively α-alkyl-β-alkoxyaldehydes.

Alkyl acetates by stoichiometric reaction of alcohols with the methylene bridged complex [Fe 2(μ-CH 2)(CO) 8

Resume The stoichiometric reaction of the methylene-bridged complex [Fe2(μ-CH2)-(CO)8] with methanol and ethanol gives methyl and ethyl acetate, respectively, in high yields. Labelling studies with CH3OD and CD3OD provide insight in the reaction steps involved.

Effet accelerateur de sels d'ammoniums quaternaires heterocycliques sur l'hydrolyse d'esters neutres par l'acetylcholinesterase et la butyrylcholinesterase

Some heterocyclic cations (1-methylacridinium, 1-methyl-2-hydroxyiminomethylpyridinium and 1-methyl-3-methoxy-pyridinium) cause acceleration of hydrolysis of alkyl acetates (methyl, ethyl or n-propyl acetate) by acetylcholinesterase (acetylcholine acetylhydrolase EC 3.1.1.7) (Barnett, P. and Rosenberry, T.L. (1977) J. Biol. Chem. 252, 7200–7206). In this study, it is shown that (a) other mono- and bisquaternary ligands of pyridinium, quinolinium and benzoquinolinium series accelerate methyl-, ethyl- and n-propyl-acetate hydrolysis by acetylcholinesterase, (b) these ligands generally accelerate methyl-, ethyl- and n-propyl-acetate, -propionate and -butyrate, 2-methoxyethyl- and furfuryl-acetate, and ethylene-glycol diacetate hydrolysis by butyrylcholinesterase (acylcholine acylhydrolase, EC 3.1.1.8). At the present time, the ability to accelerate enzymatic hydrolysis of neutral substrates appears to be restricted to some heterocyclic quaternary ammonium compounds. Acceleration which occurs at physiological ionic strength (Γ/2 = 0.155) involves ternary enzyme-substrate-ligand complex formation and interaction of ligands with the catalytic anionic subsite. It concerns the step leading to the enzyme-substrate complex formation and/or the acylation step of enzymes. Kinetic behaviour analogy of acetylcholinesterase and butyrylcholin-esterase in the presence of the same ligands suggests that an identical acceleration mechanism arises for both enzymes.

Kinetics of the Alkaline Hydrolysis of Alkyl Acetates: Solvent Effects

Kinetics of the Alkaline Hydrolysis of Alkyl Acetates: Solvent Effects

Microdetermination of ether lipids by the isotopic derivative technique

Complex mixtures of ether lipids and ester lipids are subjected to reduction with lithium aluminiumhydride to yield 1-alkylglycerols, 1-alk-1'-enylglycerols, and alcohols. Acetylation of these reduction products with radioactively labelled acetic anhydride leads to mixtures of alkyldiacetylglycerols, alk-1-enyldiacetylglycerols, and alkyl acetates. These derivatives are resolved by thin-layer chromatography and then estimated by scanning of the chromatogram or by liquid-scintillation counting of the eluted fractions.

Kinetics of the Alkaline Hydrolysis of Alkyl Acetates: Solvent Effects

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Hydrogen bond assisted reactions of carboxylic acids with alkyl halides in the gas phase by ion cyclotron resonance spectroscopy

The reactions of the strongly hydrogen bonded anions, CH3CO2HF− and (CH3CO2)2H−, with alkyl halides have been studied in the gas phase by ion cyclotron resonance spectroscopy. A novel reaction of nucleophilic attack by (CH3CO2)2H− with alkyl chlorides to produce CH3CO2HCl− and alkyl acetates is reported. Parallels are drawn to synthetically important analogous reactions in glacial acetic acid solutions of alkali metal fluorides.