Unreactive Solvents

A typical cationic polymeriza tion is conducted with highly purified monomer free of moisture and residual alcohol, both of which act as inhibitors, in a suitably dry unreactive solvent such as toluene with a Eriedel-Crafts catalyst, eg, boron triduoride, aluminum trichloride, and stannic chloride. Usually low temperatures (—40 to —70°C) are favored in order to prevent chain-transfer or sidereactions. 

If a drybox is not available, the preparation can also be carried out by use of a dry, unreactive solvent (typically an alkane) as a blanket against hydrolysis. This has been suggested in the patent literature as a method for the large-scale industrial preparation of Eewis acid-based ionic liquids, as the solvent also acts as a heat-sink for the exothermic complexation reaction [28]. At the end of the reaction, the ionic liquid forms an immiscible layer beneath the protecting solvent. The ionic liquid may then either be removed by syringe, or else the solvent may be removed by distillation before use. In the former case it is likely that the ionic liquid will be contaminated with traces of the organic solvent, however. 

The stoichiometry of the redox reactions of conducting polymers (n and m in reactions 1 and 2) is quite variable. Under the most widely used conditions, polypyrroles and polythiophenes can be reversibly oxidized to a level of one hole per ca. 3 monomer units (i.e., a degree of oxidation, n, of ca. 0.3).7 However, this limit is dictated by the stability of the oxidized film under the conditions employed (Section V). With particularly dry and unreactive solvents, degrees of oxidation of 0.5 can be reversibly attained,37 and for poly-(4,4 -dimethoxybithiophene), a value of n = 1 has been reported.38 Although much fewer data are available for n-doping, it appears to involve similar stoichiometries [i.e., m in Eq. (2) is typically ca. 0.3].34,39"41 Polyanilines can in principle be reversibly p-doped to one... 

Following a reductive dechlorination in ether, a violent explosion occurred when ethyl acetate was added to decompose excess aluminate [1]. Ignition was attributed to the strongly exothermic reaction occurring when undiluted (and reducible) ethyl acetate contacts the solid aluminate. Addition of a solution of ethyl acetate in inert solvent or of a moist unreactive solvent to destroy excess reagent is preferable [2], See reference 1-7, above... 

Benzene is recognized as a very unreactive solvent, especially for triplet carbenes. Therefore, the most reactive reactants under these conditions must be the triplet carbenes themselves. However, the products obtained from the photolysis in benzene consist of a highly complex mixture containing small amounts of car-bene dimers. It is then possible that the simple dimerization of brominated DPCs must suffer from severe steric repulsion and, therefore, the carbene is forced to react at other positions. The most probable reactive sites are the aromatic rings, where spin can be delocalized. 

Ethyl Acetate. Explosion occurred when ethyl acetate was used to destroy excess LiAlH4 either a solution of ethyl acetate in an inert solvent or a moist unreactive solvent should be used.9... 

Dissociation of acyinitrenes occurs, presumably from the triplet state, when carbonylnitrenes are produced in very unreactive media, or in a vacuum. Ethoxycarbonylnitrene, produced by flash photolysis in vacuo, dissociates to "NCO and EtO, the former being identified by its detailed and intense u.v. absorption spectrum. The NCO radical is not produced, however, when cyclohexene vapour is present. In this case, the normal double bond adduct, 7-ethoxycarbonyl-7-azabi-cyclo[4.1.0]heptane is formed, as identified by its i.r. spectrum . Pivaloylnitrene, i-BuCO—N, when produced in unreactive solvents, such as dichloromethane or neopentane, apparendy dissociates in a similar manner. A polymer suggested as being the product from <-Bu and NCO is formed, and isobutene can be obtained in 22% yield (based on nitrene formed) when a stream of nitrogen is passed through the reaction mixture . ... 

Electrochemical reduction of azobenzenes in DMF in the presence of succinyl chloride gives pyridazinediones in fair yield [128] a similar reaction with azomethine or nitroso compounds gave low or no yield of heterocyclic compounds. The reactions require dry media and unreactive solvent systems the reaction type may be illustrated by Eq. (20) ... 

Photolysis of (if 5-C5H5)(if 2-C2H4)2Rh in the presence of benzene in an unreacting solvent such as pentane yields a remarkable product having the following characteristics. 

Macroporous resins. In contrast to gel-type resins, these are prepared by polymerization in an unreactive solvent, which defines the pore structure. The functionality is largely restricted to the pore surface and is accessible even to solvents and liquid reaction media that are not good sweUing solvents. 

As investigations of their solution photochemistry have proliferated, it has become increasingly clear that it is nearly impossible to find a completely unreactive solvent for some diones. Thus, for example, the quantum yield for disappearance of phenanthrenequinone in degassed benzene solution at 4358 A is 0.25 131> (perfluoro compounds, which might indeed be unreactive, are extremely poor solvents for many diones). 

Benzoic acid prepared catalytically from phthalic anhydride may contain certain undesirable compounds, tars, and coloring materials and must of necessity be purified in some cases to obtain a marketable product. Naphthoquinone impurities are reduced to naphthohydroquinones by treatment of the product with sulfur dioxide or sodium bisulfite at 40° to 50° C. for 3 to 4 hours. Any phthalic anhydride remaining is converted to phthalic acid at the same time. Leaching with water is used to remove the reduced impurities.72 Unconverted phthalic acid may also be separated from benzoic by treatment of the mass with sodium carbonate so as to convert the polycarboxylic acid into a primary salt while leaving the mono-carboxylic acid unreacted. Solvent leaching is then used to separate the salt from the acid.78 Colored impurities in benzoates from synthetic benzoic acid may be removed by oxidation with potassium permanganate.71... 

Reports of the products formed from photolysis of phenyl azide in unreactive solvents at or near room temperature presented a confusing picture until it was discovered that the result obtained depends critically on the concentration of the azide and the power of the light source. In essence, only two products are obtained from the irradiation of phenyl azide in oxygen free, inert solvents such as hexane or acetonitrile tarry polymer and azobenzene. Very little, if any, of the anilines observed in high-temperature thermolysis of the azide are obtained. 

I think that the discovery that he could make complexes which were soluble in non-polar and relatively unreactive solvents such as benzene (more widely used in those days than now) and diethyl ether (tetrahydrofuran did not become readily available until the late 1950s) proved to be a particularly important observation, because it opened up the possibility of doing meta-... 

If anhydrous ammonia is reacted, at about room temperature or below, with /3-propiolactone in certain unreactive solvents, good yields of /3-alanine are obtained. Solvents such as alcohols, esters, ketones, and aliphatic nitriles can be used. For example, a yield of about 97 per cent is obtained by adding gaseous ammonia gradually to a solution of /3-propiolactone in acetonitrile, cooled to 3-7°C. The /3-alanine formed precipitates from the acetonitrile solution. A practically pure product is obtained by filtering from the solvent, washing with ether, and drying. When the reaction is run in teri-butanol at 30 C, the yield is about 82 per cent. 

Polymers made by batch and semibatch processes can also be stripped of unreacted solvents and monomers by processing through equipment described above, but commonly they are purihed by vacuum stripping. In vacuum stripping, volatile solvents are pulled out at the end of the batch as much as possible. Initially the amount of solvent recovered is high however, as the solids content increases, the melt viscosity increases and the rate of solvent recovered declines. 

The solution, having been made stable in the can, must now be made reactive on the coated surface. In the case of unsaturated polyesters, this is done by introducing factor (3) in relatively large quantities. This is an initiator (p. 65). In thermally cured, as opposed to radiation cured finishes, the substance chosen to decompose and produce free radicals is an organic peroxide. A solution of this material in unreactive solvent forms the activator pack of the two-pack finish. The amount of solvent is chosen to give a suitable finish/activator mixing ratio, e.g. 10 1 by volume. The ketone, diacyl and hydroperoxide types are most frequently used. 

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