Water-HMPA

The influence of concentration and type of supporting electrolyte [49, 52] and also temperature [50] on the Zn(II) electroreduction was investigated in water-DMSO and water-HMPA mixtures. The change of kinetic parameters under the influence of these factors was similar to that observed in pure aqueous solutions. 

It was concluded that the change in the kinetics of the Cd(II)/Cd(Hg) system with mixed solvent composition may be described by different model equations in water-DMSO [61], and water-HMPA solvents [62]. 

In contrast to oxidation in water, it has been found that 1-alkenes are directly oxidized with molecular oxygen in anhydrous, aprotic solvents, when a catalyst system of PdCl2(MeCN)2 and CuCl is used together with HMPA. In the absence of HMPA, no reaction takes place(100]. In the oxidation of 1-decene, the Oj uptake correlates with the amount of 2-decanone formed, and up to 0.5 mol of O2 is consumed for the production of 1 mol of the ketone. This result shows that both O atoms of molecular oxygen are incorporated into the product, and a bimetallic Pd(II) hydroperoxide coupled with a Cu salt is involved in oxidation of this type, and that the well known redox catalysis of PdXi and CuX is not always operalive[10 ]. The oxidation under anhydrous conditions is unique in terms of the regioselective formation of aldehyde 59 from X-allyl-A -methylbenzamide (58), whereas the use of aqueous DME results in the predominant formation of the methyl ketone 60. Similar results are obtained with allylic acetates and allylic carbonates[102]. The complete reversal of the regioselectivity in PdCli-catalyzed oxidation of alkenes is remarkable. 

Hexametbyipbospboric triamide (HMPA) [680-31-9] M 179.2, f 7.2°, b 68-70°/lmm, 235°/760mm, d 1.024, n 1.460. The industrial synthesis is usually by treatment of POCI3 with excess of dimethylamine in isopropyl ether. Impurities are water, dimethylamine and its hydrochloride. It is purified by refluxing over BaO or CaO at about 4mm pressure in an atmosphere of nitrogen for several hours, then distd from sodium at the same pressure. The middle fraction (b ca 90°) is collected, refluxed over sodium under reduced pressure under nitrogen and distd. It is kept in the dark under nitrogen, and stored in solid CO2. Can also be stored over 4A molecular sieves. 

Prior to tlie advent of tripbenylpbospbine-stab dized CuH [6a, b, 11], Tsuda and Saegusa described use of Gve mole percent MeCu/DtBAL in THE/HMPA to effect bydtoaluminaiion of conjugated ketones and esters [26], Hie likely aluminium etiolate intermediate could be quendied witli water ot TMSCl, ot alkylated/acylated widi various electrophiles fsudi as Mel, allyl bromide, etc. Sdieme 5.5). Mote... 

THF (10 ml) was added to the above solution of TMSLi in HMPA, and the mixture immediately cooled to —78°C. A solution of cyclohex-2-enone 1.5mmol) in THF (1ml) was then added dropwise. After stirring for an additional 5 min, methyl iodide (0.5 ml, excess) was added, and the mixture allowed to warm slowly to 0°C. It was then poured into pentane (50 ml) and washed thoroughly with water (2 x 25 ml). After drying and concentration, the residual oil was distilled to give trans-3-trimethylsilyl-2-methylcyclo-hexanone (97%), b.p. 80°C/1 mmHg (Kugelrohr). 

A solution of LDA (11 mmol) in THF (30 ml) was cooled to -78°C, and HMPA (CAUTION—CANCER SUSPECT AGENT) (3 ml) then added. To this solution was added dropwise 3-acetoxyoct-l-ene (10 mmol), and then TBDMSC1 (11 mmol) in THF (2 ml) over 5 min. The pale yellow solution was stirred at -78°C for an additional 2 min, and the reaction mixture was allowed to warm to 25DC over 30min. It was stirred at this temperature for a further 2 h, and then quenched with water and pentane. The combined pentane extracts were concentrated, the crude oily silyl ester was dissolved in THF (25 ml) and dilute aqueous HC1 (5 ml, 3 m) and the solution was then stirred for 45 min at 25 °C to complete hydrolysis. The mixture was then poured into aqueous sodium hydroxide (30 ml, I m) and... 

Alkyl halides can be hydrolyzed to alcohols. Hydroxide ion is usually required, except that especially active substrates such as allylic or benzylic types can be hydrolyzed by water. Ordinary halides can also be hydrolyzed by water, if the solvent is HMPA or A-methyl-2-pyrrolidinone." In contrast to most nucleophilic substitutions at saturated carbons, this reaction can be performed on tertiary substrates without significant interference from elimination side reactions. Tertiary alkyl a-halocarbonyl compounds can be converted to the corresponding alcohol with silver oxide in aqueous acetonitrile." The reaction is not frequently used for synthetic purposes, because alkyl halides are usually obtained from alcohols. 

Room-temperature solution polycondensation is used for the preparation of hexafluoroisopropylidene-unit-containing poly(azomethine)s. At the end of the reaction, the water liberated by the reaction is thoroughly taken off as an azeotrope by vacuum distillation to allow the reaction to go to completion. Among DMF, DMSO, HMPA, NMP, and m-cresol used as reaction solvents, m-cresol yields a polymer with higher reduced viscosity in higher yield. The reaction proceeds rapidly and is essentially completed in 30 min. 

The allenylindium intermediates are prepared by treatment of the aziridines with Pd(PPh3)4 in THF-HMPA containing 1 equivalent of water. In the presence of iso-butyraldehyde the expected adducts were formed with excellent diastereoselectivity (Tables 9.56 and 9.57). Interestingly, the reaction did not proceed in the absence of water. It is suggested that water is needed to protonate the sulfonamide anion of the initially formed allenyl palladium species (Eq. 9.150). 

Kemp et al., 1978). The rate is slowest in an aqueous solution and is enhanced in aprotic and/or dipolar solvents. The rate augmentation of 106—108 is attainable in dipolar aprotic solvents such as dimethyl sulfoxide and hexamethylphosphoramide (HMPA). Interestingly, the decarboxylation rate of 4-hydroxybenzisoxazole-3-carboxylate [53], a substance which contains its own protic environment, is very slow and hardly subject to a solvent effect (1.3 x 10-6 s-1 in water and 8.9 x 10-6 s-1 in dimethylformamide Kemp et al., 1975). The result is consistent with the fact that hydrogen-bonding with solvent molecules suppresses the decarboxylation. 

All the above reactions of PVC were performed homogeneously in DA-solvents such as HMPA, DMF and dimethylsulfoxide (DMSO). For the practical modification of PVC, the reaction must be conducted under more commercial conditions as in slurry water. As mentioned before, azidation of PVC did not occur in water. However, the reaction proceeded feasibly in water by addition of some cationic surfactant to give, e.g. 8-20% (DS) of azidated PVC at 80°C by use of tetra-n-butyl ammonium chloride (1 ). The use of cationic surfactant was also effective in organic solvents and attracted increased attention as the conception of "phase transfer catalyst" in organic chemistry developed. 

Thioetherification of PECH is feasibly performed in DA-solvents as already described in the patent (20J. For example, the highest substitution was obtained by the reaction of P(ECH-EO)(1 1 copolymer of epichloro-hydrin and ethylene oxide) and equimolar thiophenoxide in HMPA at 100°C for 10 h as DS 83% for sodium and 93% for potassium salts. The DS in our nucleophilic substitution was estimated by the elemental analysis as well as the titration of liberated chloride ion with mercuric nitrate (21). In the latter method, reacted medium was pretreated with hydrogen peroxide when the reductive nucleophiles which can react with mercuric ion were used. As described before for PVC, thiolation was also achieved conveniently with iso-thiuronium salt followed by alkaline hydrolysis without the direct use of ill-smelling thiolate. The thiolated PECH obtained are rubbery solids, soluble in toluene, methylene chloride, ethyl methyl ketone and DMF and insoluble in water, acetone, dioxane and methanol. 

The formation of S-alkyl thiosulfate (Bunte salt) by the reaction of alkyl halide and sodium thiosulfate has been well known. Whereas a patent claimed the formation of Bunte salt from PECH and sodium thiosulfate (23), the reaction hardly proceeded in DMF owing to low solubility of sodium salt. On the other hand, both ammonium thiosulfate and PECH were soluble in HMPA-H20 (7 1 vol/vol) and the reaction proceeded homogeneously. Water soluble Bunte salt (j2, v(S0), 1200, 1020 cm-1) was isolated by pouring the reaction mixture into water and salting out with ammonium chloride. The DS based on the mercuric nitrate titration was in nearly accord with that on elemental analysis. The DS values depended on the thiosulfate concentration were shown below. 

In Table 6 the differences of free enthalpies of solvation for several anion ligands in a donor solvent D and in AN are given. HMPA shows very weak solvation whereas water is a very strong solvating agent for anions. The free enthalpies of solvation of halide and pseudohalide ions are by 4 to 15 keal/mol more negative than in aprotic donor solvents. 

The presence of water may have an appreciable effect onE j, since water is a fairly strong donor. It is known that it is extremely difficult to remove the last traces of water from any solvent and it is therefore of interest to know the influence of water. It is apparent that in solution of a strong donor such as DMF, DMA, DMSO or HMPA the presence of small amounts of water is not reflected in a shift of the half-wave potential. On the other hand, the half-wave potential is shifted to negative potential values by the presence of water in a weak donor solvent. 

Stabilization by a solvent can often determine the very initial step consists of ion-radical generation. Hence, alkali metal hydroxides are highly stabilized in water and in aqueous organic solvents, and therefore, their reactivities in simple one-electron processes are either very low or practically nonexistent. Alkali-metal hydroxides are at least somewhat soluble, particularly in the presence of water traces, in polar solvents (DMSO, HMPA, THF). In these solvents, the HO solvation is drastically diminished (Popovich and Tomkins 1981). As a result, reactions of one-electron transfer from the hydroxy anion to the substrate take place (Ballester and Pascual 1991). 

Clean the Erlenmeyer flask with deionized water and let it dry. Add 14.3 grams (or 0.25 moles) of activated zinc dust and 80 mL of HMPA to the dried flask. Stir to mix. Next, add 32 mL of chlorotrimethylsilane (equivalent to 0.24 mol). Stir the mixture for 90 minutes at room temperature. Cool the mixture on ice for 20 minutes. 

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