3768.     ---------------.  [ZIMMERSCHIED, W. J., DINERSTEIN, R. A., WEITKAMP, A. W., AND MARSCHNER, R. F.]  Crystalline Adducts of Urea With Linear Aliphatic Compounds.  A New Separation Process.  Ind. Eng. Chem., vol. 42, 1950, pp. 1300-1306; Chem. Abs., vol. 44, 1950, p. 9356.

        With n-alkanes and their linear derivatives, urea forms crystalline complexes; with most branched and cyclic hydrocarbons and their derivatives, it does not.  The effects of time, concentration of urea, concentration of urea solvent, concentration of n-alkane, and volume of wash liquid were studied, and optimum conditions were applied in the separation of unbranched hydrocarbons from complex petroleum  fractions.  Compounds such as 2-bromoöctane, where substitution occurs at a point other than the end of a linear chain, often do not yield urea adducts.  No simple molecular ratio of urea to C atoms was determined.  An empirical value of 0.8±0.1 for the ratio was found for chains 7-32 C atoms long.  The heats of adduct formation were measured for straight chain paraffins, olefins, alcohols, bromides, mercaptans, and Me esters.  From a comparison of this heat with the heats of crystal transition, fusion, vaporization, H bonding, adsorption, and gas hydrate formation, urea adduct formation resembles adsorption more closely than any other physical process.  Petroleum fractions usually contain inhibitors to adduct formation.  This was overcome by the use of an activator such as MeOH, or by seeding with freshly prepared adduct.  Formation of the adduct at room temperature is reasonably rapid, and recovery of the components by heating or stirring with H₂O is virtually quantitative.

        ZISSON, J.  See abs. 3153a.

        ZOLOTOV, M. N.  See abs. 1107.