Magnesium secondary

Phenols. Phenols are unreactive toward chloroformates at room temperature and at elevated temperatures the yields of carbonates are relatively poor (< 10%) in the absence of catalysis. Many catalysts have been claimed in the patent Hterature that lead to high yields of carbonates from phenol and chloroformates. The use of catalyst is even more essential in the reaction of phenols and aryl chloroformates. Among the catalysts claimed are amphoteric metals or thek haUdes (16), magnesium haUdes (17), magnesium or manganese (18), secondary or tertiary amines such as imidazole (19), pyridine, quinoline, picoline (20—22), heterocycHc basic compounds (23) and carbonamides, thiocarbonamides, phosphoroamides, and sulfonamides (24). 

Potassium-sparing by diuretic agents, particularly spironolactone, enhances the effectiveness of other diuretics because the secondary hyperaldosteronism is blocked. This class of diuretics decreases magnesium excretion, eg, amiloride can decrease renal excretion of potassium up to 80%. The most important and dangerous adverse effect of all potassium-sparing diuretics is hyperkalemia, which can be potentially fatal the incidence is about 0.5% (50). Therefore, blood potassium concentrations should be monitored carehiUy. 

The reaction of alcohols and acid chlorides in the presence of magnesium has been described (68). With primary and secondary alcohols the reaction is very smooth, and affords high and sometimes quantitative yields. Difficulty esteritiable hydroxy compounds such as tertiary alcohols and phenols can be esteritied by this method. The reaction carried out in ether or benzene is usually very vigorous with evolution of hydrogen. 

Comparison of the results obtained by the redrying procedure with those by the primary reference method (room temperature, in vacuo over magnesium perchlorate) is shown in Table II. The agreement of the two sets of results was within 0.2% or better, which is considered satisfactory and serves to confirm the suitability of the redrying procedure as a secondary reference standard. 

The fact that the initial setting process for magnesium oxychloride cements takes place without observable formation of either the 5 1 8 or the 3 1 8 phase is important. It indicates that formation of an amorphous gel structure occurs as the first step, and that crystallization is a secondary event which takes place from what is effectively a supersaturated solution (Urwongse Sorrell, 1980a). This implies that crystallization is likely to be extremely dependent upon the precise conditions of cementition, including temperature, MgO reactivity, heat build-up during reaction and purity of the components in the original cement mixture. 

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