Higher boiling solvents

Choice of Solvent. In general, a higher boiling solvent is preferable to a low-boiling solvent, as evaporation is then considerably less. 

A higher-boiling solvent, e.g., 1,1,2-trichloroethane, can be used which still gives acetone a negative deviation from Raonlt s law =... 

Use of a higher boiling solvent may reduce the normal operating pressure of a process, and will also reduce the maximum pressure resulting from an uncontrolled or runaway reaction (Wilday, 1991). 

The most reliable method of preparing benzofuroxans is by decomposition of o-nitrophenyl azides. Decomposition can be achieved by irradiation, or more usually by pyrolysis temperatures between 100° and 1.50° are commonly used. Refluxing in glacial acetic acid is the recommended procedure for 4- or 5-sub-stituted 2-nitrophenyl azides, but with 3- or 6-substituted compounds higher boiling solvents are usually necessary. Quantitative studies on the reaction rate have been made, and a cyclic transition state invoked, an argument which has been used to account for the greater difficulty of decomposition of the 6-substituted 2-nitrophenyl azides. Substituent effects on the reaction rate have also been correlated with Hammett a constants, ... 

The material exploded when the temperature of evaporation of the slurry was increased by adding a higher-boiling solvent. This may have been caused by presence of some of the tautomeric ac/-nitro-o-thioquinone. Such salts are thermally unstable. 

The rate of reaction is markedly solvent-dependent. In the higher-boiling solvents re-octane, ethylcyclohexane, and cfs-1,2-dimethyl cyclohexane the reaction is much faster, but prolonged reflux in these solvents causes extensive decomposition. Some typical results are the following re-octane, 1.75 hours, 64% yield ethylcyclohexane, 2.0 hours, 60% yield. 

Triphenylacetic acid is not reduced under ordinary conditions in the medium of ether. But it is converted into a primary alcohol in good yield either by reduction in higher boiling solvent like THF or by first converting it into an acid chloride which is then readily reduced in ether. 

When higher boiling solvents such as cyclohexane are used, the reaction is complete earlier, but side-products can be detected that are difficult to remove from the. reaction mixture and that tend to catalyze decomposition of the desired product. 

Similarly the cation (18a), which does not react with alkoxides [75JCS(P1)1260], is protodebrominated by triphenylphosphine, albeit a higher boiling solvent, pentan-l-ol, is required to promote the reaction. The salt (18c), which cannot form a dihydrodiazepine base, also undergoes protodebromination when heated with triphenylphosphine in pentan-l-ol [81AG193, 81AG(E)190]. 

Ref L). Used as a solvent and as a flash point retarder for hydrocarbons and higher boiling solvents... 

Reactions that are known to require high temperatures and higher boiling solvents can be carried out under pressure at these temperatures, but in lower boiling solvents, facilitating work-up. 

The bimolecular reductive coupling of carboxylic esters by reaction with metallic sodium in an inert solvent under reflux gives an a-hydroxyketone, which is known as an acyloin. This reaction is favoured when R is an alkyl. With longer alkyl chains, higher boiling solvents can be used. The intramolecular version of this reaction has been used extensively to close rings of different sizes, e.g. paracyclophanes or catenanes. 

A second approach takes full advantage of the retention gap by the addition of a small amount of cosolvent. The cosolvent is a higher-boiling solvent compared to the bulk eluent and serves to trap the volatiles while the bulk solvent evaporates. Thus, the sample is focused and the chromatography starts with sharp bands of analyte. The effects of the cosolvent and concurrent solvent evaporation have been reviewed [132], along with the minimum temperature need for concurrent solvent evaporation [133]. 

Bisoxadiazoles are formed from bis(mono)imido ester hydrochlorides and mono(bis)carboxylic acid hydrazides when the free ester is used, an amidrazone (27) is often formed which cyclizes with the elimination of ammonia to give 28.73 The reaction proceeds in the presence of higher boiling solvents or by mixing the reactants at a temperature higher than 100°, the imido esters forming first in the reaction mixture. The reaction of semicarbazide [Eq. (2), R = NH2] with imido esters does not, of course, lead to 2-amino-1,3,4-oxadiazoles but to the isomeric l,2,4-triazolin-3-ones.72 The reaction of N-substituted imidochlorides with aromatic acid hydrazides in the... 

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