Hydroxyl group relative reactivities

The solubility parameter is about 19.2MPa and being amorphous they dissolve in such solvents as tetrahydrofuran, mesityl oxide, diacetone alcohol and dioxane. Since the main chain is composed of stable C—C and C—O—C linkages the polymer is relatively stable to chemical attack, particularly from acids and alkalis. As already mentioned, the pendant hydroxyl groups are reactive and provide a site for cross-linking. 

The actual position of the linkages in a branched polymer, such as (2), will depend on the relative reactivities of the hydroxyl groups. These reactivities are known to be different both in monomeric and polymeric carbohydrates.28 In a study24 of the condensation polymerization of undo) W. II. Carothers, Trans. Faraday Soc., S3, 39 (1936) Chem. Rev., 8, 353 (1931) Ref. 12, pp. 31—132. 

Silica Gel. Silica gel is prepared by the precipitation of a silicate solution with acid, or by hydrolysis of silicon derivatives. The surface area and diameter of the silica gel particles depend on the method of precipitation. Variations in pH during precipitation can produce silica gels with surface areas ranging from 200-800 m /g. It has been shown [4] that silica gel provides three types of surface hydroxyl groups Bound, reactive, and free. Relative reactivity and adsorption follow the order bound > free > reactive. Thus, control of the distribution of surface functions can have a significant effect on the chromatographic properties of a silica. 

Neopentyl glycol, or 2,2-dimethyl-1,3-propanediol [126-30-7] (1) is a white crystalline soHd at room temperature, soluble ia water, alcohols, ethers, ketones, and toluene but relatively iasoluble ia alkanes (1). Two primary hydroxyl groups are provided by the 1,3-diol stmcture, making this glycol highly reactive as a chemical intermediate. The gem-A methy configuration is responsible for the exceptional hydrolytic, thermal, and uv stabiUty of neopentyl glycol derivatives. 

Reaction of 4,6 l/2-di-0-isopropyhdenesucrose in pyridine—chloroform with 3.3 molar equivalents of benzoyl chloride at 0°C eventually produced 3/6 -di-O-benzoylsucrose (36%) as the major and 3/4/6 - and 3,3/6 -tribenzoates as the minor products. The relative reactivities of the hydroxyl groups toward benzoylation was HO-3 HO-6 > HO-4 > HO-3 (55). 

Sulfonate Esters. Sucrose sulfonates are valuable intermediates for the synthesis of epoxides and derivatives containing halogens, nitrogen, and sulfur. In addition, the sulfonation reaction has been used to determine the relative reactivity of the hydroxyl groups in sucrose. The general order of reactivity in sucrose toward the esterification reaction is OH-6 OH-6 > OH-1 > HO-2. 

Reaction of 2,4,7-trichloroquinoline with sodium methoxide (65°, 30 min) yielded an equal mixture of 2,7-dichloro-4-methoxy- (40%) and 4,7-dichloro-2-methoxy-derivatives (31%). The activating effect of the chloro groups is evident from the inertness of 4-chloro-quinoUne to methoxide ion at 65°. Alteration of the relative reactivity by cationization of the azine ring is again noted here in the acid-catalyzed hydrolysis (dilute HCl, 100°, 1.5 hr) of the trichloro compound to give 72% of the 2-hydroxylation product.Similarly, acid-hydrolysis of the alkoxy group proceeds much more readily in 2-ethoxy-4-chloro- than in 4-ethoxy-2-chloro-quinoline. ... 

As noted in an earlier section of this article, the utility of the cycloamyloses as covalent catalysts is limited by the low reactivity of the catalytically active hydroxyl groups at neutral pH s and by the relatively slow rates of deacylation of the covalent intermediates. In an effort to achieve effective catalysis, several investigators have attempted to selectively modify the cycloamyloses by either (1) introducing an internal catalyst to facilitate deacylation or (2) introducing a more reactive nucleophile to speed acylation and/or deacylation. 

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