Carboxylic acid compounds, melting point

Structurally similar compounds often exhibit large differences in their melting points. This is illustrated in Figure 10.4.1 by comparing Tm of aromatic aldehydes and analogous carboxylic acid compounds. Structurally, the compounds differs by merely... 

A solution of 3-acetamino-adamantane-l-carboxylic acid (3.0 g) in 4 N sodium hydroxide (40 ml) was refluxed for 5 h. After cooling, the pH of the solution was adjusted to 7 with acetic acid. The crystalline precipitate was filtered off, washed with ethanol and dried to yield 2.20 g of the desired compound, melting point over 330°C. In order to purify the compound, 2.0 g of it was suspended in water (10 ml), 4 N NaOH (2 ml) was added, and the resulting solution filtered through a filter aid known under the registered trademark Dicalite. The filtrate was adjusted to a pH of 6.5 with acetic acid. The resulting crystalline precipitate was filtered off, washed with a little water followed by alcohol, and dried to yield 1.55 g of pure 3-amino-adamantane-l-carboxylic acid. 

Moreover, PHB thermally decomposes at temperatures just above its melting point. A short exposure of PHB to temperature near 180°C could induce a severe degradation accompanied by the production of the degraded products of olefinic and carboxylic acid compounds, e.g., crotonic acid and various oligomers through the random chain scission reaction that involves a cis-elimination reaction of/3-CH and a six-member ring transition [16-18]. 

The melting points and boiling points of carboxylic acids are higher than those of hydro carbons and oxygen containing organic compounds of comparable size and shape and indicate strong mtermolecular attractive forces... 

The organic layer wasdried with anhydrous magnesium sulfate and then filtered. The solution was concentrated under vacuum at 30°C to 35°C until reduced to half of its original volume and then cooled to 5°C to allow the crystallization of the compound. Thus, the cake was filtered, washed with cool ethyl acetate, and dried under vacuum. Yield 74% (76.7 g) of phthalidyl ester of 2-(3 -trifluoromethylanilino)-pyridin-3-carboxylic acid, melting point 165°C to 167°C. 

Lithium compounds are used in ceramics, lubricants, and medicine. Small daily doses of lithium carbonate are an effective treatment for bipolar (manic-depressive) disorder but scientists still do not fully understand why. Lithium soaps—the lithium salts of long-chain carboxylic acids—are used as thickeners in lubricating greases for high-temperature applications because they have higher melting points than more conventional sodium and potassium soaps. 

Table 2-1 lists some examples of carboxylic acid imidazolides of various structures prepared by the use of A -carbonyldiimidazole (CDI), A -thiocarbonyldiimidazole (Im-CS-Im), and A -sulfinyldiimidazole (Im-SO-Im). Independent of the specific method applied, the data in Table 2-1 show that reasonable yields of imidazolides and diimidazolides are quite general, irrespective of various substituents and of steric factors. The rather mild reaction conditions also permit the formation of imidazolides of highly unsaturated systems. As a further advantage, it should be mentioned that almost all imidazolides are crystalline compounds, which can be conveniently handled. Melting points are therefore included for the imidazolides listed in Table 2—1. 

Normally, amino acids exist as dipolar ions. RCH(NH,+ iCOO-. in a neutral state, where both amino and carboxyl groups are ionized. The dipolar form, RCH(NH2)COOH may be considered, but the dipolar form predominates for the usual monoamino monocarboxylic acid and it is estimated that these forms occur 10s to 106 times more frequently than the non-polar forms. Amino acids decompose thermally at what might be considered a relatively high temperature (200-300°C). The compounds are practically insoluble in organic solvents, have low vapor pressure, and do not exhibit a precisely defined melting point. 

Diphenyl selenide di-p-carboxylic acid, Se(C6H4.C02H)2, is the principal constituent of the mother-liquors from the preceding compound its melting-point varies from 312° 313° C. to 315° 316° C. 

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