Isomerization solvents

Regardless of substrate and solvent, isomerization fell in the order 5% Pd-on-C 5% Rh-on-C > 5% Pt-on-C, and, regardless of substrate or catalyst, isomerization fell with solvent in the order ethanol > pentane > 1 1 benzene-ethanol. Benzene is effective as an isomerization inhibitor mixed with other solvents as well 1 20 benzene-acetone showed marked inhibition. Substituted benzenes are less effective than benzene. 

Numerous implications on the fundamental chemistry of coal liquefaction can be drawn from the observed reaction of solvent isomerization and adduction. The literature indicates that... 

As a result, nitroalkene (42a) is almost completely isomerized into N-oxide (47a), which is stable up to 100°C (167). Isomerization proceeds smoothly both in solutions and the solid state. The isomerization rate is approximated by the first-order equation and depends on the polarity of the solvent (isomerization in hexane occurs 70 times more slowly than that in ethanol). 

The behavior of dihydroazirenoquinoxalines in solvents possessing different polarity in the presence of acids such as HC1, HBr, HI, HC104, HBF4 and CF3COOH was studied in [114]. It was shown that even under mild conditions, i.e., HC1, aprotonic solvent, isomerization into the 2-benzylquinoxaline derivatives 109 took place (Scheme 1.30). The authors could not isolate the salts as they had made for azirenoimidazoles and azirenopyrazines [88, 112]. On the basis of the experiments carried out, as well as previous data [112], a conclusion... 

The complexes of platinum(IV), less well known than those of platinum(II), can be prepared by oxidation of the latter. Such a conversion often proceeds with retention of configuration. Early workers reported that halogenation of either cis- or irans-dihalobis(dialkyl sulfide)platinum(II) resulted in only one product. The compound obtained by Loir and R y and Bose-R y by treating diethyl sulfide with aqueous or alcoholic H2[Pt(OH)2Cl4] was probably mainly the trans isomer. The preparation given here, based on the work of Angell, Drew, and Wardlaw, involves the chlorination of cis- and benzene solution. In this nonpolar solvent, isomerization is minimized. 

Regioselective dimerization of propene to 2,3-dimethylbutenes (DMBs) is currently operated by Sumitomo and BP Chemicals. Both use P(cyclohexyl)3 as the bulky ligand. In the Sumitomo process [7] very high selectivities in DMBs (up to 85 %) are obtained at 20-50 °C, thanks to a sophisticated, highly efficient, Ziegler-type catalyst system (ten times more efficient than those of conventional catalysts) and by using toluene as a solvent. Isomerization of 2,3-dimethyl-1-butene (DMB-1) into 2,3-dimethyl-2-butene (DMB-2) takes place directly in... 

E.Z -photoisomerization of the fluorinated l-phenyl-4-carboalkoxybutadienes 21 proceeds regioselectively about the phenyl-substituted double bond, consistent with the Dauben intermediate . Saltiel and coworkers have reported a particularly interesting example of solvent- and substituent-dependent regioselectivity in the E.Z-photoisomerization of , , -l,6-diaryl-l,3,5-hexatrienes (22) the quantum yields for isomerization about the central double bond in the parent molecule (22 X = H) are insensitive to solvent polarity, while those for isomerization about a terminal bond are enhanced seven-fold in acetonitrile compared with hydrocarbon solvents". Isomerization of the substituted derivatives proceeds regioselectively to yield the 1-Z and 3-Z isomers, and in both cases the quantum yield for terminal bond isomerization is enhanced dramatically in polar solvents. The results were explained in terms of competing torsional relaxation about the central and terminal bonds via biradicaloid and zwitterionic twisted intermediates, respectively. For the parent and cyano derivatives, the latter is polarized in the same sense proposed by Dauben and Ritscher. Interestingly, the polarization appears to be reversed in the case of the methoxy derivative. 

The formation of the four-membered ring is explained by an anionic rearrangement accompanied by ring contraction . The isomerization of cyclotri- and cyclodisila-zanes depends on the conditions . The substitution of silylgroups is preferred at low T in diglyme as solvent . Isomerization reactions are observed at higher T, e.g., at -i-60°C in diglyme ... 

Isomerization reactions of allylic halides ((2), X = halogen) are well known (ref. 99, p, 720), and occur in both aprotic and protic solvents. Isomerizations which accompany solvolysis reactions of allylic chlorides are discussed in Section 2.2.2. 

If one would evaporate away most of this solvent, isomerization can be done very easily by the action of KOH in alcohol. The procedure can be found in the Journal of the Chemistry Society, Volume 139, page 1168 and 1440 (1936). 

Hydrate isomerism requires water to play two roles, as (1) a ligand and as (2) an additional occupant (or solvate) within the crystal structure. Solvent isomerism broadens the definition to allow for the possibility of ammonia or other ligands participating as solvates. 

The absolute stereochemistry of a series of 9,10-dihydro-9,10-ethanoanthracenes has been established. Those such as (17) show strong Cotton effects at ca. 270 nm (a negative Lj, transition of As ca. 3) and at ca. 215 nm (a positive band with Ae ca. 60). These result from the chirality of the substituted skeleton substituents on the ethano-bridge have small effects. The results accord completely with the recent theory of Hagashita. Those such as (18) show feeble Cotton effects which are difficult to interpret. The solvent dependence of the c.d. of a number of bicyclic terpenoid alkenes has been re-examined. Band positions were solvent dependent but could not be correlated with the solvent density as had been suggested in 1973. When perfluoro-alcohols are used as solvent, isomerization may occur. 

Reaction of [Co(NH3)5( OH)] + ion with acetyl perchlorate in trimethyl phosphate solution gives [Co(NH3)5( OCOMe)] + ion. However, in more polar solvents isomerization to the [Co(NH3)5(OC OMe)] ion occurs, and during purification (by recrystallization) it is necessary to avoid polar solvents like HjO to prevent the linkage isomerization. At room temperature 32% rearrangement occurs in the solid phase after 90 days. ... 

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