Decomposition points

Distillation under Reduced Pressure. Occasionally a liquid, when distillation is attempted under atmospheric pressure, will undergo partial or complete decomposition before its boiling-point is reached. To overcome this difficulty, the liquid is distilled under reduced pressure, so that its boiling-point shall be definitely below its thermal decomposition point. 

Identification of Amines. Picric acid combines with many amines to give crystalline picrates, of general formula B,(NO )aCeHjOH, where B is a molecule of a monacidic base. These picrates have usually sharp melting- or decomposition-points, and serve to characterise the amines concerned. They may be formed either by (a) direct union of the acid and the base in a suitable solvent, or (6) by the interaction of sodium picrate and a salt of the amine in aqueous solution. 

The melting points of the derivatives of a number of amino acids are collected in Table 111,132. Most a-amino acids decompose on heating so that the melting points would be more accurately described as decomposition points the latter vary somewhat with the rate of heating and the figures given are those obtained upon rapid heating. 

These melting points are probably better described as decomposition points their values will depend somewhat upon the rate of heating. 

The melting points of carbohydrates (sugars) are not usually sharp and they are perhaps best expressed as decomposition points. 

Acetylsalicylic acid decomposes when heated and does not possess a true, clearly-defined m.p. Decomposition points ranging from 128° to 135° have been recorded a value of 129-133° is obtained on an electric hot plate (Fig. II, 11, 1). Some decomposition may occur if the compound is recrystaUised from a solvent of high boiling point or if the boiling period during recrystallisation is unduly prolonged. 

Polymerization and GycliZation. Acetylene polymerizes at elevated temperatures and pressures which do not exceed the explosive decomposition point. Beyond this point, acetylene explosively decomposes to carbon and hydrogen. At 600—700°C and atmospheric pressure, benzene and other aromatics are formed from acetylene on heavy-metal catalysts. 

Since the pinacol decomposes near its melting point the latter will vary with the rate of heating. The temperatures reported here were obtained by slow heating if the tube is placed in a bath at 150° and heated rapidly, the observed melting or decomposition point is 193-195 . 

Amino acids have high melting or decomposition points and are best examined for purity by paper or thin layer chromatography. The spots are developed with ninhydrin. Customary methods for the purification of small quantities of amino acids obtained from natural sources (i.e. l-5g) are ion-exchange chromatography (see Chapter 1). For general treatment of amino acids see Greenstein and Winitz [The Amino Acids, Vols 1-3, J.Wiley Sons, New York 1961] and individual amino acids in Chapters 4 and 6. 

After the reaction, 1 ml of water was added to the reaction mixture, and the mixture was adjusted to a pH of 1,0 with concentrated hydrochloric acid while being cooled, and then stirred for 30 minutes. The insoluble matters were filtered off, and the filtrate was adjusted to a pH of 5.5 with triethylamine. This solution was concentrated under reduced pressure, and the residue was diluted with 20 ml of acetone to precipitate white crystals. The crystals were collected by filtration and washed with ethanol to obtain 1.46 g of white crystals of7-[D(-)-0 -emino-(4-hydroxyphenyl)acetamido]-3-methyl-3-cephem-4-carboxylicacid having a decomposition point of 197°C. 

After completion of the reaction, the reaction mixture was made alkaline by the addition of sodium carbonate, whereupon crystals separated out in situ. The crystals were recovered by filtration, washed with water and then recrystallized from 6 ml of ethanol, to give 0.1 g of the pale yellow pure desired product having a decomposition point of 125°C. 

The decomposition point is obtained in a sealed capillary tube and is not corrected. As the solid is heated, it first changes from yellow to brownish red and then decomposes to a dark red liquid. The decomposition temperature of this compound has been reported to be 208.5°,4 224-225°,5 and 225-230°. ... 

Aryl group Yield, based on ArNJ Decomposition point Amax e... 

The checkers observed a decomposition point of 198-202° for the crude acid, 211-214° for the purified acid. 

Absolute ethanol (400 ml.) is vigorously stirred in a 1-1. widenecked Erlenmeyer flask immersed in an ice bath (Note 4). The tropylium hexachlorophosphate-tropylium chloride double salt4 is separated from the reaction mixture by suction filtration, washed briefly with fresh carbon tetrachloride, and transferred as rapidly as possible into the cold, well-stirred ethanol (Note 5). The salt dissolves rapidly and exothermally to give a reddish solution. Fifty milliliters (0.39 mole) of 50% aqueous fluoboric acid is added rapidly to the cold stirred solution (Note 6). The dense white precipitate of tropylium fluoborate that forms is separated by suction filtration, washed with a little cold ethanol and with ether, and air-dried at room temperature (Note 7) weight 34-38 g. (80-89%) decomposition point about 200° A j, HC1 218 mja (log e 4.70), 274 m/i (log e 3.61). The product is 98-100% pure (Notes 8 and 9). 

The melting points of carbohydrates (sugars) are not usually sharp and they are perhaps best expressed as decomposition points, t The small capital letter prefix refers to configuration, relat to D- lyceraldehyde, and not to the direction of optical rotation. The sign of optical rotation is expressed as (+) and (—) or as d and I or by the words dtxtro and loevo. Thus we have d-(—)-fructose and ,-(+).arabinose. 

The presence of impurities can cause a shift in the dissociation point. It implies that the equilibrium temperature and pressure of the carbonate decomposition reaction are shifted. The effect of silica is particularly illustrative in the case of limestone. If silica is present as an impurity, it lowers the decomposition point of limestone. The acid anhydride silica slags combines with the basic calcium oxide according to following ... 

Toxic intermediate products are produced during hydrolysis. Approximate half-life in water at 25°C is 1.3 min. Decomposition comes through slow change into quaternary ammonium salts. Decomposition point is below 94°C. 

Approximate half-life in water at 25°C is 4 min decomposition point is below boiling point. 

Subsequent DTA investigation showed that an exothermic reaction set in above 75°C after an induction period depending on the initial temperature and concentration of reactants, which attained nearly 300°C, well above the decomposition point of the cyclic ester component (170°C). The reaction conditions used could have permitted local over-concentration and overheating effects to occur, owing to slow dissolution of the clumped solid ester and aniline in the nitrobenzene solvent [ ] Crude carbyl sulfate contains excess sulfur trioxide [2]. 

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