Roughness salt effect

As has been noted above, there is no gross change in the mechanism of nitration of PhNH3+ down to 82 % sulphuric acid. The increase in o- andp-substitution at lower acidities has been attributed differential salt effects upon nitration at the individual positions. The two sets of partial rate factors quoted for PhNH3+ in table 9.3 show the effect of the substituent on the Gibbs function of activation at the m- and -positions to be roughly equal for reaction in 98 % sulphuric acid, and about 28 % greater at the -position in 82 % sulphuric acid. ... 

We may now understand the nature of the change which occurs when an anhydrous salt, say copper sulphate, is shaken with a wet organic solvent, such as benzene, at about 25°. The water will first combine to form the monohydrate in accordance with equation (i), and, provided suflScient anhydrous copper sulphate is employed, the effective concentration of water in the solvent is reduced to a value equivalent to about 1 mm. of ordinary water vapour. The complete removal of water is impossible indeed, the equilibrium vapour pressures of the least hydrated tem may be taken as a rough measure of the relative efficiencies of such drying agents. If the water present is more than sufficient to convert the anhydrous copper sulphate into the monohydrate, then reaction (i) will be followed by reaction (ii), i.e., the trihydrate will be formed the water vapour then remaining will be equivalent to about 6 mm. of ordinary water vapour. Thus the monohydrate is far less effective than the anhydrous compound for the removal of water. 

Concentration. Concentration by thermal evaporation markedly reduces the heat stability of milk, e.g. concentrated skim milk containing about 18% total solids coagulates in roughly 10 min at 130°C. The stability of the concentrate is strongly affected by pH, with a maximum at around pH 6.6, but stability remains low at all pH values above about 6.8 (Figure 9.20). Concentration by ultrafiltration has a much smaller effect on HCT than thermal evaporation, due to a lower concentration of soluble salts in the retentate. 

The reactions of thiocyanogen may roughly be divided into two types (1) Reactions in which the radical combines directly with metals to form the corresponding thiocyanates, and with cuprous thiocyanate to form the cupric salt. (2) Reactions in which a substitution is effected for example, with aniline, dimethylaniline and phenol, the corresponding jj-thiocyano-derivatives and thiocyanie acid are formed.1... 

Structure maker ions increase the concentration of micelles and reduce the concentration of monomers. In a very rough model one can assume the fixed hydration sphere around the ions cannot solve the ethylenoxide products and increase its concentrations in the rest bulk water phase (salt-out effect). In this model one can estimate the size of the hydration sphere of the ions. The hydration numbers gained by this method are surprisingly large3 They start at 200 water molecules per ion pair at 0.1 mole solutions of ions and decrease about 20 at 1 mole solutions31,72,130). 

Selective reduction of ot,a-dihalo ketones." Reduction of a,a-dihalo ketones can he effected without hydrogenolysis of the halo groups with either DIBAH or borane dimethyl sulfide. Reactions with the former reagent are generally faster but work-up can be complicated by gelatinous aluminum salts. In general, the yields are roughly comparable. 

---