Desiccant efficiency in solvent and reagent drying. 7. Alcohols

Burfield, David R.; Smithers, Roger H.

doi:10.1021/jo00162a026

Cited by 67 publications

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“…Because the common technique for controlling water activity with saturated salt solutions was not suitable for this reaction system, molecular sieves were used to remove the water formed in the reaction. Molecular sieves have been shown to dry t-butyl alcohol to a water content of 13 ppm but only at a slow rate, thought to be dependent on its relatively high viscosity (14). To ensure a water activity as low and constant as possible throughout the reaction, the sieves were exchanged as the reaction proceeded and as water accumulated.…”

Section: Resultsmentioning

confidence: 99%

Antioxidative properties and enzymatic synthesis of ascorbyl FA esters

Viklund

Alander²,

Hult

2003

J Americ Oil Chem Soc

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Efficient synthesis of unsaturated FA esters of ascorbic acid is possible with only a small excess of one of the reactants in t-amyl alcohol using Candida antarctica lipase as biocatalyst. Using free acids, we obtained yields that were comparable to yields reached using vinyl-activated acyl donors (71, 80, and 86% yields of esters with FA excesses of 1:1, 1:1.5, and 1:2, respectively). As very low water activity is needed to achieve sufficiently high yields of product, molecular sieves were used to improve the ascorbyl ester yields. Ascorbyl oleate is more amorphous and has a much lower m.p. and lower enthalpy of fusion than ascorbyl palmitate. This leads to a higher solubility of ascorbyl oleate in oil, resulting in an increased antioxidant effect compared to that of the palmitate. In an accelerated storage test using deodorized rapeseed oil, samples incubated with ascorbyl palmitate showed noticeable oxidation after 1 wk of storage, whereas samples incubated with ascorbyl oleate displayed negligible oxidation for 9 and 4 wk at 30 and 40°C, respectively.Paper no. J10512 in JAOCS 80, 795-799 (August 2003).Ascorbyl palmitate is a fat-soluble antioxidant commonly used in foods to prevent oxidation of sensitive fats and oils. Ascorbyl palmitate has a disadvantage, however, in that it has relatively low solubility in oils. The solubility can be improved by the addition of lecithin, although this causes the product to become hygroscopic. Another way to improve the solubility of an ascorbyl FA ester is to modify its structure to make it less crystalline. This can be done, for example, by introducing a double bond in the FA. Oleic acid is unsaturated, readily available, inexpensive, and approved for use in foods. This makes it an attractive candidate to replace the palmitic acid in an ascorbyl ester. The chemical synthesis of saturated ascorbyl FA esters is straightforward (1). A similar procedure for the synthesis of ascorbyl oleate has been described in the literature (2) but has proven hard to repeat. The difficulties are due to the double bond of oleic acid, which is too sensitive for the reaction conditions needed for the chemically catalyzed esterification. Enzymatic catalysis, however, can be performed at lower reaction temperatures and under milder conditions, enabling the enzymatic synthesis of ascorbyl oleate (Scheme 1). Because the reactants differ in polarity, the number of suitable solvents available is limited. We used t-amyl alcohol because it dissolves the reactants at high concentrations and does not deactivate the enzyme.In 1971, Arakawa et al.(3) reported on the first enzymatic synthesis of ascorbyl laurate in aqueous solution. In 1990, Enomoto et al. (4) filed a patent on the esterification in organic solvents, and esterfications in t-amyl alcohol were reported by Humeau et al. (5) in 1995. Since then, not only saturated FA have been used, but also various unsaturated FA (6-8) as well as of phenyl butyric acid (9) and methyl lactate (10). These syntheses have typically reached yields below 50% unles...

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Section: Resultsmentioning

confidence: 99%

Antioxidative properties and enzymatic synthesis of ascorbyl FA esters

Viklund

Alander²,

Hult

2003

J Americ Oil Chem Soc

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“…All aromatic and hydrocarbon solvents used were distilled from sodium benzophenone ketyl and stored under nitrogen over 4 A molecular sieves. Alcohols were purchased from Aldrich Chemical Co. and were dried by disti!lation from magnesium turnings under dinitrogen and stored over 4 A molecular sieves (13). Infrared spectra were recorded on a Perkin-Elmer Model 1620 spectrometer, and NMR data were recorded on Bruker AC-250 spectrometer.…”

Section: Methodsmentioning

confidence: 99%

Solid state and solution structural investigation of homoleptic tin(IV) alkoxide compounds. Part I. Sn(O—t-Bu)₄ and [Sn(O—i-Pr)₄•HO—i-Pr]₂

Hampden‐Smith¹,

Wark²,

Rheingold³

et al. 1991

Can. J. Chem.

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. Can. J. Chem. 69, 121 (1991).The crystal and molecular structures of s n ( % t -B~)~ and [Sn(&i-Pr)4.H&i-Pr]2 have been determined by single-crystal X-ray diffracti9n. Sn(&t-Bu)40crystallizes in the monoclinic crystal system with space group C2/c, where a = 17.382(6) A, [Sn(&i-Pr)4.H&i-Pr]2 exhibits an edge-shared, bi-octahedral structure in the solid state that is distorted due to the presence of asymmetric hydrogen bonding between axially coordinated alcohol ligands and an isopropoxide ligand. I3C NMR and IR spectroscopic data have been recorded for Sn(&t-Bu)4 and S n ( & t -B~-d~)~ to establish criteria for unambiguous identification of solution structures of tin(1V) alkoxides. It is demonstrated that the two-bond 2~~j C -&~~9 s n coupling constant is larger for terminal alkoxide ligands than for k2-alkoxide bridges, and the v(Sn-0) stretching frequency has been assigned. The dynamic solution behaviour of [Sn(&i-Pr)4.H&i-Pr]2 has been studied using variable temperature 'H and I3C NMR spectroscopy. The data obtained are consistent with a process that involves rapid reversible dissociation of isopropanol at room temperature. Upon cooling, the equilibrium concentration of the species with coordinated alcohol increases, and the molecule undergoes rapid intramolecular proton transfer (AG* < 11.9 kcal mol-I). Upon further cooling, the I3C NMR data are consistent with a solution structure analogous to that found in the solid state.Key words: tin, alkoxide, NMR, dynamic, structure. travers deux liaisons 2~~lC-&ttssn, est plus grande pour les ligands alcoolates terminaux que pour les ponts alcoolates-k2; de plus, on a attribut la frtquence de,. Faisant appel a la rmn du 'H et du I3c, a temperature variable, on a ttudit le comportement dynamique du [Sn(%i-Pr).HO--i-Pr] en solution. Les donntes obtenues sont en accord avec un processus qui implique une dissociation reversible rapide de l'isopropanol, a la temptrature ambiante. Par refroidissement, la concentration de l'espkce avec de I'alcool isopropylique augmente et la moltcule subit un transfert intramoltculaire rapide de proton (AG* < 1 1,9 kcal mol-I). Si on continue le refroidissement, les donntes de la rmn du I3c obtenues sont en accord avec une structure en solution qui serait analogue a celle qui est trouvte a l'ttait solide.

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“…All hydrocarbon and ethereal solvents were dried and distilled from sodium benzophenone ketyl. Alcohols were dried by distillation from magnesium turnings [11]. NMR solvents were dried over 4A molecular sieves and stored under N 2 .…”

Section: Methodsmentioning

confidence: 99%

Molecular Routes to Tin Oxides

et al. 1990

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A general route to low temperature synthesis of ternary metal tin oxides with controlled stoichiometries from single component molecular metal alkoxide precursors is described. The solid state and solution structures of homoleptic tin(IV) alkoxide compounds have been investigated to establish criteria for the determination of their solution structure. Tin alkoxide compounds suitable for metathesis reactions have been synthesized and used to prepare the mixed metal alkoxide compounds [ZnSn(OEt) 6 ] and [((COD)Rh) 2 Sn(OEt)6] (where Et = ethyl and COD = 1,5-cyclooctadiene). Hydrolysis of [ZnSn(OEt)6] at neutral pH results in the formation of a high surface area, mainly amorphous hydrous oxide powder which forms Zn2SnO 4 and SnO2 on heating to 600 0 C and ZnSnO3 on heating to 1000 0 C.Thermolysis of [ ((COD)Rh } 2 Sn(OEt) 6 ] results in formation of rhodium and tin(IV) oxide (cassiterite phase).

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Desiccant efficiency in solvent and reagent drying. 7. Alcohols

Abstract: Acknowledgment. We are grateful to Professor Samuel Danishefsky, Yale University, for encouragement and support through Grant No. AI 16943-03.Registry No. 1, 2, 3, (+)-pulegone, 89-82-7.

Cited by 67 publications

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Antioxidative properties and enzymatic synthesis of ascorbyl FA esters

Antioxidative properties and enzymatic synthesis of ascorbyl FA esters

Solid state and solution structural investigation of homoleptic tin(IV) alkoxide compounds. Part I. Sn(O—t-Bu)₄ and [Sn(O—i-Pr)₄•HO—i-Pr]₂

Molecular Routes to Tin Oxides

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Desiccant efficiency in solvent and reagent drying. 7. Alcohols

Abstract: Acknowledgment. We are grateful to Professor Samuel Danishefsky, Yale University, for encouragement and support through Grant No. AI 16943-03.Registry No. 1, 2, 3, (+)-pulegone, 89-82-7.

Cited by 67 publications

References 0 publications

Antioxidative properties and enzymatic synthesis of ascorbyl FA esters

Antioxidative properties and enzymatic synthesis of ascorbyl FA esters

Solid state and solution structural investigation of homoleptic tin(IV) alkoxide compounds. Part I. Sn(O—t-Bu)4 and [Sn(O—i-Pr)4•HO—i-Pr]2

Molecular Routes to Tin Oxides

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Solid state and solution structural investigation of homoleptic tin(IV) alkoxide compounds. Part I. Sn(O—t-Bu)₄ and [Sn(O—i-Pr)₄•HO—i-Pr]₂