Cholesterol was crystd. under various conditions from a range of solvents, and the effects of the solvents on the crystal structure were studied. The phase transitions and the latent heat, $Δ$Hp, were measured and were found to vary from 0.18 kcal mole-1 (for CCl4) to 1.1 kcal mole-1 (for acetonitrile). It seems possible that the polymorphic transitions of cholesterol at 37° may be divided into several subtransitions, each one corresponding to a slight configurational change that can be attributed to a possible flip-over of the aliph. chain of the cholesterol. [on SciFinder(R)]

Polycarboxylic amino acids were examd. as possible retarding agents in the pptn. of urinary Ca oxalate [563-72-4] calculi. The effect was obsd. by continuous detn. of the concn. of Ca ions in a mimic urine soln. Both Na polyglutamate [26247-79-0] and Na polyaspartate [34345-47-6], when used in concns. of 5-100 ppm, significantly retarded Ca oxalate pptn. [on SciFinder(R)]

The effect of solvents on the crystal structure of pure stearic acid crystd. from them was studied using x-ray and DTA. The latent heat of the phase transition, $Δ$Ht, was measured for the two well-defined forms B and C. X-ray diffractograms are the means for the identification of crystal modifications. However, only qual. information about the compn. present in the mixt. is inferred from the relative peak intensities. DTA of the phase transitions at 54° (for B) and 64° (for A) furnishes quant. data for each component present in the mixt. Values of 0 and 4.9 cal g-1 for the phase transition enthalpies were measured for the pure C form and B form, resp. Intermediate values were found for mixts. of C and B. The interplay between the crystn. conditions (type of solvent, cooling rate, and flow regime) dictates the formation of various crystal structure modifications. [on SciFinder(R)]

A salt water slurry of Dunaliella parva, an halophilic alga, was treated to convert it into C6H6-sol. material, as rich as possible in C and H. Several features obsd. were: 25% of the combined C can be extd. under mild conditions of pressure (atm.) and temp.; the presence of CO as well as transition-metal salts has only minor effect on the conversion and the compn. of the product; and ≤75% of the combined C is converted by in-situ presence of C6H6 during the pyrolysis of the alga-salt water slurry. [on SciFinder(R)]

A new method is described for following the inhibitory effect in artificial urine of polymeric dicarboxylic amino acids and other polyanionic derivs. on Ca oxalate crystn. The technique is based on using a Ca-specific electrode to measure Ca++ ion activity in soln. to assess the formation of Ca oxalate ppt. The retardation effect of poly-L-glutamic acid Na salt and poly-L-aspartic acid Na salt occurred in a 5-100 ppm concn. range. Blocking of the free carboxylic groups on the polymers eliminated the retardation effect. The retardation appears to be an inhibition of seed crystal growth rate. Normal urine retarded the pptn. but pathol. urine did not. [on SciFinder(R)]

Kinetics and stereochem. of Rh/Al2O3-catalyzed hydrogenations of p-(Me3C)2C6H4 (I), p-(Me3C)2C6H4 (II), Me3CPh (III), and p-MeC6H4CMe3 (IV) were studied as models for the mechanism of hydrogenation of benzene rings. At approx. atm. pressure, the rates are 0 order in arene, 1st order in H and increased in the order III, I \textless IV \textless II. In competition expts. the order of reactivity is III \textgreater IV \textgreater I \textgreater II. The formation of cyclohexene-type intermediates, dependent on increased pressure, was discussed. A dissociative mechanism due to bulky CMe3 groups was rejected; the orientation of the CMe3 groups, however, affect both the rate of hydrogenation and the proportion of products formed via subsequent alternate reaction paths. [on SciFinder(R)]

The reactive sites on platinum metal catalysts for the hydrogenation of unsatd. hydrocarbons and related reactions were the most coordinatively unsatd. exposed metal atoms. The surface atoms were divided into 3 groups with one, two, or three units of coordinative unsatn. (corresponding to the no. of monodentate ligands which may become attached) and were symbolized by 1M, 2M, and 3M, then, when exposed to H the 1st structures formed were 2MmH2 and 3MH2, which were transformed, in part, to 2MH and 3MH by diffusion of H from the edge to other surface sites or to the interior of the crystallite. The proportions of 3M and 3MH present during a reaction were a function of the metal and the conditions of prepn. and use. These structures bore a formal relation to the structure of the complexes ClRh(PPh3)2 (I) and HRhCO(PPh3)2 (II) which are formed through the dissocn. of ClRh(PPh3)3 and HRh(CO)(PPh3)3, resp. The catalytic functions of both I and II involved the same kinds of elementary processes, but the presence of the hydrido group in II led to recognizably different phenomena (kinetics, stereochem., exchange reactions). Accordingly, the characteristics of hydrogenations catalyzed by platinum metals may be rationalized by considering the elementary processes which may occur at each category of site. [on SciFinder(R)]

Hydrogenation of 1,4- (I) and 1,3-di-tert-butylbenzene (II), p-xylene (III), and m-xylene (IV) over a Rh/Al2O3 catalyst at 0.34-150 atm H pressure was examd. With I, the rate of hydrogenation, the amt. of intermediate cyclohexene formed, and the cis-trans ratio of final product all increased, then decreased, with increasing pressure, but with II the rate and amt. of intermediate increased, while the product cis-trans ratio decreased, with increasing pressure. Hydrogenation of III paralleled that of I, except that the cis-trans ratio of dimethylcyclohexane steadily increased with increasing pressure; the same pressure effect on product isomer distribution was obtained with IV, but with IV the rate of hydrogenation increased with pressure throughout the obsd. range. The results are discussed in terms of possible types of reactive sites and their interconversion. [on SciFinder(R)]

Diimide, generated from azodicarboxylic acid at 25°, was used to reduce a series of cycloalkenes and cycloalkadienes (C5-C8, C12). In agreement with redns. with diimide conducted at 80°C by Garbisch, Schildcrout, Patterson, and Sprecher (1965), the relative reactivity of the monoenes fall in the order norbornen »C8(cis) \textgreater C5 \textgreater C7 \textgreater C6; however, the spread in rates is greater in the present study. Compared to cyclohexene, the relative reactivity of C8(trans) and norbornene are 2200 and 700, resp., at 25°. 1,3-Cyclohexadiene is more reactive than cyclohexene; however, the cyclo-C5, cyclo-C7, and cyclo-C8-1,3-dienes are less reactive than the monoene each forms on redn. Although conjugation tends to lower the reactivity of a diene, torsional strain, which serves here as a driving force, may reduce the planarity of a conjugated system, as in 1,3-cyclohexadiene, and thus the conjugative interaction as well. [on SciFinder(R)]

Symmetrization of ArHgX with EDTA and NH3 24 hr at room temp. in aq. or org.-aq. mixts. gave 40-95% Ar2Hg (Ar = p-Br-, p-Cl-, p-AcNH-, p-NHMe-, Me, p-Et2N-, p-Me2N-, p-MeOC6H4; Ph; m-xylyl, pseudocumyl, pentamethylphenyl, duryl, isoduryl, mesityl, and $\alpha$-naphthyl). Other nucleophiles (e.g. BuNH2) were as effective as NH3, but EDTA was the best chelating agent. [on SciFinder(R)]

The mechanism for the symmetrization of arylmercuric salts in the presence of chelating agents includes 3 main steps: (i) dissocn. of the arylmercuric salt; (ii) formation of a reactive complex between the ionized arylmercuric salt and the chelating agent; (iii) an electrophilic substitution at a C-Hg bond via a 2-electron, 3-center bond type transition state. The effect of chelating agents on the reactions of PhHgOAc with piperidine, BuNH2, or CNS- to give Ph2Hg and of m-MeC6H4HgOAc with tetra-Na ethylenediaminetetraacetate to give (m-MeC6H4)2Hg was discussed. [on SciFinder(R)]

Treatment of 4 compds. of the type Ar(HgX)2 and of poly[4-(acetoxymercurio)styrene] with EDTA tetra-Na salt [64-02-8] and NH3 [7664-41-7] resulted in symmetrization and polymn. of the monomers and crosslinking of the polystyrene [9003-53-6] by Hg [7439-97-6]. E.g., 2,5-bis(chloromercurio)thiophene gave poly(mercurio-2,5-thiophenediyl) [57715-35-2]. [on SciFinder(R)]

A high yield recyclization and pollution free process for the manuf. of diarylmercury compds. is described. The new process enables saving of starting materials and recovery of Hg. [on SciFinder(R)]