Toluene in hexane solution

The resolving power of an instrument is controlled by its slit width settings. For some pharmacopoeial tests a certain resolution is specified. The resolving power of an instrument can be assessed by using a 0.02% w/v solution of toluene in hexane. The BP specifies that the ratio of the absorbance for this solution at 269 nm to that at 266 nm should be at least 1.5. 

Tests. A solution mixture of 0.02% v/v toluene in hexane (UV grade) is used to test the resolution power of the spectrophotometer. Hexane as the reference is scanned and then the spectrum of the resolution solution from 250 to 300 nm is obtained. The absorbance values of the Amax at 269 nm and the Amin at 266 nm are recorded (Figure 10.7). 

The dimer exists in two stereoisomeric forms, the proportion of which varies with the solvent used (24). The quantum yield in toluene varies with concentration, and indicates that the photoreaction involves processes 3,4, and 15, together with processes analogous to 5 + 8 involving the triplet and not the singlet excited level (10). No quantitative studies have yet been made of the fact that the chief product in hexane solutions is probably the cis isomer and in benzene solution the trans. 

We have recently studied laser ablation of graphite and Ceo particles suspended in solutions [6,7]. It was found that hydrogen-capped polyynes (C2 H2 = 4-8) were produced from graphite particles suspended in benzene, toluene, or hexane solution [6], while C2 H2 (n = 4-6) polyynes were formed from Cgo in hexane or methanol solution [7]. Cataldo [8,9] has recently synthesized C2 H2 (n = 2-9) polyynes by a submerged electric arc discharge in organic solvents. 

The reciprocal dispersion for a grating-based system is therefore essentially constant with respect to wavelength. SBW in the UV region can be determined by measuring a solution of 0.02% toluene in hexane using a matched hexane reference cell. The absorbance is measured at both 268.7 and 267.0 nm. The ratio of absorbances (A268.7( 267.o) is calculated and is directly related to the SBW, as shown in Table 2.11 (Figure 2.26). 

Interfdci l Composite Membra.nes, A method of making asymmetric membranes involving interfacial polymerization was developed in the 1960s. This technique was used to produce reverse osmosis membranes with dramatically improved salt rejections and water fluxes compared to those prepared by the Loeb-Sourirajan process (28). In the interfacial polymerization method, an aqueous solution of a reactive prepolymer, such as polyamine, is first deposited in the pores of a microporous support membrane, typically a polysulfone ultrafUtration membrane. The amine-loaded support is then immersed in a water-immiscible solvent solution containing a reactant, for example, a diacid chloride in hexane. The amine and acid chloride then react at the interface of the two solutions to form a densely cross-linked, extremely thin membrane layer. This preparation method is shown schematically in Figure 15. The first membrane made was based on polyethylenimine cross-linked with toluene-2,4-diisocyanate (28). The process was later refined at FilmTec Corporation (29,30) and at UOP (31) in the United States, and at Nitto (32) in Japan. 

In contrast to the hydrolysis of prochiral esters performed in aqueous solutions, the enzymatic acylation of prochiral diols is usually carried out in an inert organic solvent such as hexane, ether, toluene, or ethyl acetate. In order to increase the reaction rate and the degree of conversion, activated esters such as vinyl carboxylates are often used as acylating agents. The vinyl alcohol formed as a result of transesterification tautomerizes to acetaldehyde, making the reaction practically irreversible. The presence of a bulky substituent in the 2-position helps the enzyme to discriminate between enantiotopic faces as a result the enzymatic acylation of prochiral 2-benzoxy-l,3-propanediol (34) proceeds with excellent selectivity (ee > 96%) (49). In the case of the 2-methyl substituted diol (33) the selectivity is only moderate (50). 

A solution of 1.5 mol equiv of butyllithium in hexane is added to 1.5 mol equiv of a 1 M solution of hexabutylditin in THF at 0 C under nitrogen, and the mixture is stirred for 20 min. The solution is cooled to — 78 °C and a solution of 1.5 mol equiv of diethylaluminum chloride in toluene is added. After stirring for 1 h at — 78 °C, a solution of 0.05 mol equiv of [tetrakis(triphenyl)phosphine]palladium(0) in THF is added followed by a solution of the allyl acetate in THF. The mixture is warmed to r.t., and stirred until the allyl acetate has reacted (TLC). The solution is cooled to 0°C, and an excess of aq ammonia slowly added. After an aqueous workup, the products arc isolated and purified by flash chromatography on silica gel using 1 % triethylamine in the solvent to avoid acid-induced loss of stannane. 

To a solution of 310 mg (1.18 mmol) of 4-[(Z)-5-(trimethylsilyl)-3-pentenyl]-3-vinyl-2-cyclohcxcnone in 20 mL of toluene is added at —78, JC 0.75 mL (2.75 mmol) of a 50% solution of ethylaluminum dichloride in hexane. After stirring for 2 h at — 78 C. the mixture is quenched by addition of 20 mL of sat. aq NaHC Oj. After washing with 20 mL of brine the organic phase is extracted with three 30-mL portions of diethyl ether and dried over MgS04. The solvent is removed and the crude product is flash chromatographed (silica gel, EiOAc/petroleum ether 1 9) yield 114 mg (60%). 

A solution of 1.3 equiv of alkyllithium in hexane is added to a mixture of 1 cquiv of the enimine and 1.4equiv of (1 R,2R)-l,2-dimethoxy-1,2-diphenylethane8 in toluene at — 78°C. The solution is stirred at either — 78 CC or — 45 °C (see table above) for 1 -13 h and then treated with an acetate buffer (pH 4.5) for 12 h. The usual workup gives the aldehyde, which is then reduced with NaBH4 in methanol to give the alcohol. 

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