Hydroxyl group reactions

Hydroxyl Group. Reactions of the phenohc hydroxyl group iaclude the formation of salts, esters, and ethers. The sodium salt of the hydroxyl group is alkylated readily by an alkyl hahde (WiUiamson ether synthesis). Normally, only alkylation of the hydroxyl is observed. However, phenolate ions are ambident nucleophiles and under certain conditions, ring alkylation can also occur. Proper choice of reaction conditions can produce essentially exclusive substitution. Polar solvents favor formation of the ether nonpolar solvents favor ring substitution. 

Among the reactive groups in wool the most important are amino, imino, and hydroxyl groups. Reactions occur in a weakly acidic medium (pH 3-5) and include nucleophilic substitution of leaving groups (usually Cl, F, and, rarely, sulfonate or ammonium groups) or addition reactions to polar aliphatic double bonds. 

B. Numerical Methods of the Calculations of the Surface Hydroxyl Group Reaction Constants... 

The numerical optimization methods do not require additional assumptions of the temporal constancy, or even neglect some physical constants, for example surface potential. Used for the optimization of the edl parameters (surface hydroxyl group reaction constants, capacity and density of adsorption sites) the numerical methods allow us to find the closest values to the experimentally available data (surface charge density, adsorption of ions, zeta potential, colorimetric measurements). Usually one aims to find the parameters, accepted from physical point of view, where a function, that expresses square of the deviation between calculated and measured values will be the smallest. 

A separate problem, having an influence on the properties of the surface is the purity of the experimental sample. It means not only the presence of anionic or cationic impurities, but also the presence of the one crystalline form in another one. For example, the even small amounts of the anatase on the surface of the rutile may essentially change the properties of the latter. At the beginning, the edl was characterized by two values pHpzc and pHiep. The critical review of these data was made by Parfitt [164]. A comprehensive survey of pHpzc values, up to nineteenth was done by Lyklema [22]. After the site binding model was worked up, the edl is characterized by the surface hydroxyl group reaction constants. The values of these constants for TiC>2 in different solutions are presented in the papers by James and Parks and Schindler [11,16]. 

All the oligo-polyols are used to build the polyurethane high MW structure in a reactive process, as a consequence of the oligo-polyols terminal hydroxyl group reaction with polyisocyanates. The reactivity of oligo-polyols in polyurethane fabrication is a very important practical characteristic. Reactivity is a measure of the reaction rate of an oligo-polyol with an isocyanate in order to make the final polyurethane polymer. One practical method is the measurement of viscosity, in time, by Brookfield Viscosity Test (BVT), especially used to determine the reactivity of ethylene oxide capped polyether polyols. Figure 3.12 shows the effect of the primary hydroxyl content upon the reactivity of ethylene-oxide capped polyether triols of MW of 5,000 daltons. 

The first step of PO addition to hydroxyl groups is the SN-2 attack of the tertiary nitrogen atom to the a-carbon atom of the oxiranic ring, activated by a hydrogen bond between the oxiranic oxygen and hydrogen atom of hydroxyl groups (reaction 13.6). 

The alkoxylation of these structures, having carboxyl groups and hydroxyl groups, is a self catalysis process, catalysed by the acidic -COOH groups. Two simultaneous reactions take place the esterification of carboxyl groups with PO (reaction 16.14) and the etherification of hydroxyl groups (reaction 16.15) [34]. 

Castor oil and the hydrolysis product - ricinoleic acid are a source of new valuable products. Thus, by the caustic oxidation of ricinoleic acid, sebacic acid and 2-octanol are formed. By hydrogenation of sebacic acid (or better of dimethylsebacate), 12-decanediol is formed. By hydrogenation of ricinoleic acid an interesting diol is obtained 1,12 hydroxystearyl alcohol having one primary and one secondary hydroxyl group (reaction 17.11). 

Hydroxyl-group reactions, such as etherification, acetalatlon (41), esterification (42-51). and oxidation, can be done in the same manner as they are on other polysaccharides. Esterifications... 

Over the last decade, a considerable number of reactions has been studied (11,35) (i) olefins oxidation (38,39), hydroboration, and halogenation (40) (ii) amines silylation (41,42), amidation (43), and imine formation (44) (iii) hydroxyl groups reaction with anhydrides (45), isocyanates (46), epichloro-hydrin and chlorosilanes (47) (iv) carboxylic acids formation of acid chlorides (48), mixed anhydrides (49) and activated esters (50) (v) carboxylic esters reduction and hydrolysis (51) (vi) aldehydes imine formation (52) (vii) epoxides reactions with amines (55), glycols (54) and carboxyl-terminated polymers (55). A list of all the major classes of reactions on SAMs plus relevant examples are discussed comprehensively elsewhere (//). The following sections will provide a more detailed look at reactions with some of the common functional SAMs, i.e hydroxyl and carboxyl terminated SAMs. 

---