Ethers ambient concentrations

Grosjean, E D. Grosjean, R. Gunawardena, and R. A. Rasmussen, Ambient Concentrations of Ethanol and Methyl tert-Butyl Ether in Porto Alegre, Brazil, March 1996-April 1997, Environ. Sci. Technol., 32, 736-742 (1998a). 

Sodium hydride (10 mmol) dispersed in 10 ml toluene was added to phosphonoacetic acid triethyl ester (10 mmol) followed by 2-bromo-3-methoxycarbonyl-5-phthaloylimidobutyric acid methyl ester (10 mmol) dissolved in 70 ml toluene and the mixture stirred for 24 hours at ambient temperature. Thereafter, the solution was neutralized with 1 ml ethereal HCl, concentrated, purified by chromatography on silica gel with acetone/toluene, 1 1, and the product isolated as a colorless oil in 60% yield. 

The product from Stepl (0.01 mol) was dissolved in 100ml THE, 17 ml 1.6 M methyl lithium (0.03 mol) added, cooled to —20°C, and 7 ml 1 M t-butyl lithium (0.01 mol) gradually added. Dimethyl formamide (0.02 mol) was added and the mixture stirred 1 hour. After slowly warming to ambient temperature the mixture was hydrolyzed with water, poured into diethyl ether, and concentrated. The material was purified by chromatography on silica gel with petroleum ether/EtOAc, 9 1, and the product isolated. 

With aldehydes, primary alcohols readily form acetals, RCH(OR )2. Acetone also forms acetals (often called ketals), (CH2)2C(OR)2, in an exothermic reaction, but the equiUbrium concentration is small at ambient temperature. However, the methyl acetal of acetone, 2,2-dimethoxypropane [77-76-9] was once made commercially by reaction with methanol at low temperature for use as a gasoline additive (5). Isopropenyl methyl ether [116-11-OJ, useful as a hydroxyl blocking agent in urethane and epoxy polymer chemistry (6), is obtained in good yield by thermal pyrolysis of 2,2-dimethoxypropane. With other primary, secondary, and tertiary alcohols, the equiUbrium is progressively less favorable to the formation of ketals, in that order. However, acetals of acetone with other primary and secondary alcohols, and of other ketones, can be made from 2,2-dimethoxypropane by transacetalation procedures (7,8). Because they hydroly2e extensively, ketals of primary and especially secondary alcohols are effective water scavengers. 

The separation of Hquid crystals as the concentration of ceUulose increases above a critical value (30%) is mosdy because of the higher combinatorial entropy of mixing of the conformationaHy extended ceUulosic chains in the ordered phase. The critical concentration depends on solvent and temperature, and has been estimated from the polymer chain conformation using lattice and virial theories of nematic ordering (102—107). The side-chain substituents govern solubiHty, and if sufficiently bulky and flexible can yield a thermotropic mesophase in an accessible temperature range. AcetoxypropylceUulose [96420-45-8], prepared by acetylating HPC, was the first reported thermotropic ceUulosic (108), and numerous other heavily substituted esters and ethers of hydroxyalkyl ceUuloses also form equUibrium chiral nematic phases, even at ambient temperatures. 

A mixture of p-chloroanisole (0.5 mol) and PhLi (0.5 mol, prepared from PhBr and Li in ether) in ether (600 ml) was stirred at ambient temperature for 50 h. A solution of TMSCI (0.5 mol) in ether (50 ml) was added with stirring, which was continued for a further 24 h. The mixture was poured into saturated ammonium chloride solution, the layers were separated, and the ethereal layer was dried. Concentration and fractional distillation gave 4-chloro-2-trimethylsilylanisole, b.p. 84°C/2mmHg. which crystallized in the receiver. Three crystallizations from ethanol gave the pure silane (0.3mol, 60%). m.p. 51-51.5°C. 

A solution of hex-l-yne (0.3 mol) in ether (100 ml) was treated consecutively at -78 °C with a solution of n-butyl lithium (0.306 mol) in hexane and with TMSC1 (0.306 mol). The reaction mixture was brought to ambient temperature, stirred for 2h, and then quenched with ice-water. The layers were separated, and the aqueous layer was re-extracted with pentane. The combined organic extracts were washed with water and brine, and dried. Concentration and distillation gave the alkynylsilane (0.267mol, 89%), b.p. 71-73 C/36mmHg. 

Trimethylsilyloctan-4-ol. To a solution of vinyltrimethylsilane (6.77mmol) in THF (15 ml), cooled to -78°C, was added a solution of ethyllithium (8.8mmol, 1.15m in ether) with stirring. The mixture was stirred at -78 °C for 2h, warmed to -30°C over 1 h, and then cooled again to -78 °C. n-Butanal (7.5 mmol) was added, and then the reaction mixture was allowed to come to ambient temperature and stirred for 3 h. It was then partitioned between brine and ether. The layers were separated, and the organic layer was dried, concentrated and the residue distilled (oven temperature 120 °C) to give the /i-hydroxysilane (6.3 mmol, 89% based on n-butanal), as a 2 1 mixture of threo and erythro diastereoisomers. 

To (E)-stilbcnc oxide (25 mmol) in THF (35 ml) was added freshly prepared dimethylphenylsilyl lithium (25.35 mmol, 1.3 m in THF) dropwise at ambient temperature. The solution was stirred at ambient temperature for 4h, and then poured into saturated ammonium chloride solution (15ml), diluted with ether, and the separated organic layer was dried and concentrated. The crude product (97 3 (Z) (E), g.I.c.) was purified by chromatography on silica gel to give (Z)-stilbene (18.75 mmol, 75%). 

To a solution of thexyldimethylsilyl chloride (11 mmol) and ImH (15 mmol) in DMF (5 ml) was added the alcohol (11 mmol) at ambient temperature. After being stirred at ambient temperature for 16 h, the mixture was diluted with hexane. The hexane phase was washed with water (2x), and then dried. Concentration followed by distillation (Kugelrohr) gave the silyl ether (86-93%). 

To a cooled (—110X) solution of the silylvinyl lithium (from the stannylethene (37 mmol) and n-BuLi (41 mmol)) in THF (100 ml) was added precooled crushed C02 (ca. 150 ml). The mixture was stirred at — 110 X for 0.5h, and then allowed to warm to ambient temperatiire overnight. The mixture was poured into ether (200 ml) and extracted thoroughly with aqueous NaOH (1m). The basic extracts were acidified with dilute HC1 at 0°C and extracted well with ether. The ethereal extracts were dried, concentrated, and the residue was distilled to give the title acid (32 mmol, 86%), b.p. 68-74 °C/0.5mmHg. 

Boron trifluoride etherate (1 mmol) was added dropwise to a stirred solution of the epoxysilane (1 mmol) in dichloromethane (5 ml) at -78 °C, and the mixture was stirred for 5min. The reaction mixture was quenched with saturated sodium hydrogen carbonate solution (1 ml), and allowed to warm gradually to ambient temperature. The organic phase was washed with brine (3 x 5 ml), dried and concentrated. The (Z)-epoxysilane gave the (Z)-silyl enol ether (68%, 96 4(Z) (E)), and the (E)-isomer gave the (E)-silyl enol ether (69%, 95 5 ( ) (Z)). 

Base-induced elimination. KH (0.1 g, 50% slurry in oil, 1.25mmol) was washed with pentane (4 ml). To the residue was added THF (5 ml) and the alcohol (0.378mmol), and the mixture was stirred for lh at ambient temperature. It was then partitioned between ether and saturated ammonium chloride solution, and the ethereal layer was separated, dried and concentrated to give the alkenes as a 95 5 mixture of ( ) (Z) isomers, in 96% yield (g.l.c.). 

A solution of LD A (0.1 mol) inTHF (75 ml), prepared as above, was then cooled to — 78 °C, and a solution of the TMS carboxylate (0.1 mol) in THF (40 ml) was added with stirring, which was continued at —78 °C for a further 30min. Excess TMSC1 (0.5 mol) was added over 5 min, and the reaction mixture was allowed to come to ambient temperature over 30 min with stirring. It was then filtered by suction through a pad of Celite, and concentrated using a rotary evaporator. The residue was taken up in ether (50 ml), and filtration and concentration were repeated. Distillation of the residue gave the ketene bis(trimethylsilyl)acetals, ca. 90%. 

A mixture of lead(iv) acetate (20 mmol) and KOAc (100 mmol) in AcOH (30 ml) was treated with the neat aldehyde-derived silyl enol ether (20mmol) at ambient temperature. After being stirred for 1 h at ambient temperature, the reaction mixture was diluted with water (30ml), and then extracted with pentane (3 x200ml). The combined pentane extracts were washed with saturated sodium hydrogen carbonate solution (2x50ml), dried, concentrated and distilled to give the product a-acetoxyaldehyde (45-78%). 

The Grignard reagent prepared from chloromethyltrimethylsilane (30 mmol) and Mg (36 mg atom) in ether (20 ml) was added dropwise to diphenyl phosphorazidate (27 mmol) in ether (40 ml), keeping the temperature below 0°C. The reaction mixture was stirred for 2 hat 0 C, and then at ambient temperature for 3 h. It was then cooled to 0 °C, and ice-water was added. The mixture was filtered, and the solid was washed with ether. The combined ethereal extracts were washed with ice-water and dried. Careful concentration at <45 °C/atmospheric pressure, then distillation at... 

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