Colloids with acid character

A. Colloids with acid character which carry only acid groups such as —COO, —0S03 —OPOaH". 

Lecithin preparations produced in practice (without very rigorous precautions) do indeed possess I.E.P. which are very much lower than the theoretical I.E.P. (p. 294 Ch. IX 21). As a result ot the facts mentioned above they behave in the neighbourhood of the neutral point as colloids with acidic character, in which the phosphate group is the carrier of the negative charge. 

The amphoteric colloids will at very low pH behave practically as " ionised colloids with basic character at high pH just as acid colloids , while in the intermediate region positive and negative charges occur together and just equilibrate one another at the isoelectric point (I. E. P.). 

Water. The character of the water has a great influence on the character of the beer and the hardness of water (alkalinity) manifests itself by the extent of its reaction with the weak acids of the mash. Certain ions are harm fill to brewing nitrates slow down fermentation, iron destroys the colloidal stabihty of beer, and calcium ions give beer a purer flavor than magnesium or sodium ions (Table 7). 

In addition to dissolving in acids, freshly precipitated niobium pentoxide dissolves in caustic soda and in caustic potash, and hence it appears to possess weakly amphoteric character. Its colloidal state in solution has hitherto prevented any direct determination of its basicity or acidity. According to Weinland and Storz 6 it is comparable to silicic acid, and is more strongly acid than titanic add. That niobic add is a very weak add is shown by the readiness with which the niobates are (a) hydrolysed and (b) decomposed by mineral acids,... 

Adsorption onto Colloidal Particles. In addition to our studies of complexation with polymeric carboxylic acids, we have also investigated adsorption of the same end-tagged PEG on colloidal surfaces. Just as the hydrophobic or hydrophilic character of the acid can be changed, in colloidal... 

Among such oxidations, note that liquid-phase oxidations of solid paraffins in the presence of heterogeneous and colloidal forms of manganese are accompanied by a substantial increase (compared with homogeneous catalysis) in acid yield [3]. The effectiveness of n-paraffin oxidations by Co(III) macrocomplexes is high, but the selectivity is low the ratio between fatty acids, esters, ketones and alcohols is 3 3 3 1. Liquid-phase oxidations of paraffins proceed in the presence of Cu(II) and Mn(II) complexes boimd with copolymers of vinyl ether, P-pinene and maleic anhydride (Amberlite IRS-50) [130]. Oxidations of both linear and cyclic olefins have been studied more intensively. Oxidations of linear olefins proceed by a free-radical mechanism the accumulation of epoxides, ROOH, RCHO, ketones and RCOOH in the course of the reaction testifies to the chain character of these reactions. The main requirement for these processes is selectivity non-catalytic oxidation of propylene (at 423 K) results in the formation of more than 20 products. Acrylic acid is obtained by oxidation of propylene (in water at 338 K) in the presence of catalyst by two steps at first to acrolein, then to the acid with a selectivity up to 91%. Oxidation of ethylene by oxygen at 383 K in acetic acid in... 

The abnormal behaviour of the pho hatides is closely connected with the association character of these colloids. Their negative charge is due to impurities of an acid nature (probably phosphatidic acids) which are tenaciously attached to the actual phosphatide molecules by London — v. d. Waals forces. The relative amount of them compared with the actual phosphatide molecules (amphoion ) determines their colloid equivalent weight, the magnitude of their reversal of charge concentrations with cations and the position of the isoelectric point (see p. 295). 

---