References tetrahydrofuran-3-ones

These equilibria give directly only acidity differences between RH and R H and can vary with solvent and counterion. The corresponding — log f values have been converted to pK scales by choosing one compound as the standard and referring others to it. The standard chosen for tetrahydrofuran (THF) solutions is fluorene and it is assigned a pK of 22.9, its value in the DMSO scale (statistically corrected per hydrogen for fluorene the measured pK is 22.6)3,4. 

Hydroxy-4-methyl-4-penten-2-one (1) was prepared from 3-chloro-mesityl oxide using a modified procedure from the literature [ref.4], A reference sample of 4-methyl-4-penten-2,3-dione (2) was prepared from using the copper acetate method [ref.2], 4-methyl-pentan-2,3-dione (3) was purchased from Wiley Co. 2-Hydroxy-4-methyl-4-penten-3-one (4) was synthesized in 30% yield from 2-propenyl-magnesium bromide and 2-hydroxy-propionitrile in tetrahydrofurane. The structures of all compounds were confirmed by H-. C-NMR- and mass spectroscopy [ref. 5],... 

We have studied the dispersibility of several pure PVAc-styrene graft copolymers with one PS branch in various selective solvents mainly at room temperature5. The experiment was done with two kinds of dried samples one was recovered from a tetrahydrofuran solution by pouring it into water and the other from a benzene solution which was poured into n-hexane. Let us refer to the former sample as A and the latter sample as B. Due to the difference in solubility of each polymer sequence in those solvents, sample A is supposed to have approximately such a microstructure that PVAc chains are extended and PS chains collapsed, while sample B has the inverse structure. A similar tendency was also pointed out by Merrett12. The results are summarized in Table 2. 

Here [Pf ] is the concentration of growing centres ending in monomer x and kx y is the absolute rate coefficient of reaction of P with monomer y. Two difficulties arise in anionic polymerization. In hydrocarbon solvents with lithium and sodium based initiators, [Pf ] is not the total concentration of polymer units ending in unit x but, due to self-association phenomena, only that part in an active form. The reactivity ratios determined are, however, unaffected by the association phenomena. As each ratio refers to a common active centre, the effective concentration of active species is reduced equally to both monomers. In polar solvents such as tetrahydrofuran, this difficulty does not arise, but there will be two types of each reactive centre Pf, one an anion and the other an ion-pair. Application of eqn. (22) will give apparent rate coefficients as discussed in Section 4 if total concentrations of Pf are used. Reactivities can change with concentration if defined on this basis. 

The activation energy of anionic propagation in the homopolymerization of styrene was determined to be about 1 kcal. per mole. This value refers to the reaction proceeding in tetrahydrofuran solution. The activation energy for the same reaction in dioxane was reported (1, 2) to be 9 3 kcal. per mole. This is one of many examples which stresses the importance of a solvent in ionic polymerization. 

Diazotetrazole (16) was obtained by dropwise addition of 2-pentyl nitrite to a solution of 5-amino-l//-tetrazole in a 4 1 mixture of tetrahydrofuran and aqueous hydrochloric acid. The diazonium chloride can be extracted into ether. Shevlin obtained the extremely explosive solid diazonium salt (16) by evaporation of that solution. He has recommended that not more than 0.75 mmol of diazonium salt be isolated at one time. An explosion during the diazotization of 5-aminotetrazole on a laboratory scale was described by Gray and coworkers. The structure 17 (equation 5) indicates clearly that this diazo compound may have the tendency to decompose into atomic carbon and three equivalents of dinitrogen—a reaction which is clearly highly exothermic. The decomposition of the tetrazole-5-diazonium chloride (16) has been studied by Shevlin by coating the salt on the walls of a 500 ml flask in the presence of two substrates, ethene and ethylene oxide. With ethene the products found after heating the flask to 80 °C are shown in equation 6, and with ethylene oxide in equation 7. The products correspond to those found with atomic carbon formed by completely different methods (see references cited by Shevlin). 

A proton at C-6 in 2-methylcyclohexanone is less crowded than the one at C-2 and is removed faster. The resulting enolate is referred to as the kinetic enolate. The most common experimental conditions for achieving kinetic control employ lithium diiso-propylamide (LDA) as the base in an aprotic solvent such as tetrahydrofuran (THF). The temperature is kept low, typically at — 78°C. LDA is a strong, sterically hindered base, so proton abstraction at C-6 is favored. 

Propagation proceeds with complete consumption of monomer and the propagating anionic centers remain intact as long as one employs solvents such as benzene, n -hexane and tetrahydrofuran which are inactive in transferring a proton to the propagating anion. These polymerizations, referred to as living polymerizations, are terminated when desired by the deliberate addition of a proton source such as water or alcohol. 

The Li chemical shift for benzyllithium is solvent dependent with reference to internal butyllithium, it has the values 1.06 (THF), 1.47 (Et20), and 2.07 (C H ). This upfield shift, from tetrahydrofuran to benzene, goes with a reduction in the one-bond scalar coupling, from 132 to 116 Hz this was interpreted as "due to a substantial increase in anion-cation interaction with transfer of electron density from the benzyl moiety to lithium the greater the s-character of the C-H orbitals, the more p-character in the C-Li orbital" (101). 

Besides condensation reactions, the bifunctional ACPC may also be used for cationic polymerization [52-55] (e.g., of tetrahydrofuran). The polymer obtained by the method depicted in reaction (12) contains exactly one central azo bond [56] and is a suitable macroinitiator for the thermally induced block copolymerization of vinyl monomers. Initiators like ACPC are referred to as transformation agents becaiae they are able to initiate... 

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