Alcohols melting point

The freezing of liquids in vials, bottles or flasks in a liquid bath is the most common freezing method used in laboratories. As the liquid must have a low melting point, alcohol (ethanol, melting point -114 °C) cooled by C02 (boiling point -80 °C at 1 atm) is frequently used. The bath can also be cooled by refrigerated coils. 

Waxes are compounds formed by the esterification of fatty acids and complex monohydric alcohols with relatively high melting points. Alcohols found in waxes are ... 

The melting points of these esters are usually much lower than those of the corresponding 3 5 dinitrobenzoates their preparation, therefore, offers no advantages over the latter except for alcohols of high molecular weight and for polyhydroxy compounds. The reagent is, however, cheaper than 3 5 dinitrobenzoyl chloride it hydrolyses in the air so that it should either be stored under light petroleum or be prepared from the acid, when required, by the thionyl chloride or phosphorus pentachloride method. 

The melting points of derivatives of selected alcohols are collected in Table 111,27. 

S-Alkyl-iso-thiuronium picrates. Alkyl bromides or iodides react with thiourea in alcoholic solution to produce S-alkyl-iso-thiuronium salts, which yield picrates of sharp melting point ... 

Add 1 ml. of the alcohol-free ether to 0-1-0-15 g. of finely-powdered anhydrous zinc chloride and 0 5 g. of pure 3 5-dinitrobenzoyl chloride (Section 111,27,1) contained in a test-tube attach a small water condenser and reflux gently for 1 hour. Treat the reaction product with 10 ml. of 1-5N sodium carbonate solution, heat and stir the mixture for 1 minute upon a boiling water bath, allow to cool, and filter at the pump. Wash the precipitate with 5 ml. of 1 5N sodium carbonate solution and twice with 6 ml. of ether. Dry on a porous tile or upon a pad of filter paper. Transfer the crude ester to a test-tube and boil it with 10 ml. of chloroform or carbon tetrachloride filter the hot solution, if necessary. If the ester does not separate on cooling, evaporate to dryness on a water bath, and recrystallise the residue from 2-3 ml. of either of the above solvents. Determine the melting point of the resulting 3 5 dinitro benzoate (Section 111,27). 

When semicarbazide Ls heated in the absence of a carbonyl compound for long periods, condensation to blurea, NHjCONHNHCONHj, m.p. 247-250 (decomp.), may result occasionally this substance may be produced in the normal preparation of a semicarbazone that forms slowly. Biurea is sparingly soluble in alcohol and soluble in hot water, whereas semicarbazones with melting points in the same range are insoluble in water this enables it to be readily distinguished from a semicarbazone. 

Drop 1 g. of sodium into 10 ml. of ethyl alcohol in a small flask provided with a small water condenser heat the mixture until all the sodium has dissolved. Cool, and add 1 g. of the ester and 0-5 ml. of water. Frequently the sodium salt of the acid will be deposited either at once or after boiling for a few minutes. If this occurs, filter oflF the solid at once, wash it with a little absolute ethyl alcohol (or absolute methylated spirit), and convert it into the p-bromophenacyl ester, p-nitro-benzyl ester or S-benzyl-tso-thiuronium salt (for experimental details, see Section 111,85). If no solid separates, continue the boiling for 30-60 minutes, boil oflF the alcohol, allow to cool, render the product just neutral to phenolphthalein with dilute sulphuric or hydrochloric acid, convert the sodium salt present in solution into a crystalline derivative (Section 111,85), and determine its melting point. 

Add 0 -5 ml. of phenyl isothiocyanate to the distillate and shake the mixture vigorously for 3-4 minutes. If no derivative separates, crystallisation may be induced by cooling the flask in ice and scratching the walls with a glass rod. Filter off the crude product, wash it with a little 50 per nent. ethanol, and recrystaUise from hot dilute alcohol. (See Table 111,123 for melting points of phenylthiourea derivatives of amines.)... 

The melting points of a few derivatives of selected polyhydric alcohols are collected in the following table. 

Most polysaccharides are insoluble or sparingly soluble in cold water, insoluble in cold alcohol and ether, and rarely possess melting points. Only inuUn melts at about 178° (dec.) after drying at 130°. 

Of the crystalline derivatives of thiols, those formed with 3 5-dinitro-benzoyl chloride are not very satisfactory since they have, in general lower melting points than those of the corresponding alcohols (compare Section 111,27,7) and do not diflfer widely from ethyl to n-heptyl. The best results are obtained with 2 4-dinitrochlorobenzene. 

The benzoyl compounds frequently occlude traces of unchanged benzoyl chloride, which thus escape hydrolysis by the caustic alkali it is therefore advisable, wherever possible, to recrystaUise the benzoyl derivatives from methyl, or ethyl alcohol or methylated spirit, since these solvents will esterify the unchanged chloride and so remove the latter from the recrystalKsed material. Sometimes the benzoyl compound does not crystallise well this difficulty may frequently be overcome by the use of p-nitrobenzoyl chloride or 3 5-dinitro-benzoyl chloride, which usually give highly crystalline derivatives of high melting point (see Section IV,114j. 

These are crystalline compounds with sharp melting points, and possess the further advantage that their equivalent weights may be determined by dissolving in dilute alcohol and titrating with standard alkali. Nitro-phenols, however, give unsatisfactory derivatives. 

Table IV,205, contains the melting points of the derivatives of a number of commonly-occurring aromatic alcohols.

The derivative selected in any particular instance should be one which clearly singles out one compound from among all the possibilities and thus enables an unequivocal choice to be made. The melting points of the derivatives to be compared should differ by at least 5-10°. Whenever possible, a derivative should be selected which has a neutralisation equivalent as well as a melting point (e.g., an aryloxyacetic acid derivative of a phenol. Section IV,114,4, or a hydrogen S nitrophthalate of an alcohol. Section 111,25,5). 

Hydrogen bonding m carboxylic acids raises their melting points and boiling points above those of comparably constituted alkanes alcohols aldehydes and ketones... 

Meclizine Hydrochloride. Pipera2ine Antivert, and Bonine are trade names for mech2ine dihydrochloride monohydrate [31884-77-2] (20). It is a white or slightly yellowish crystalline powder with a slight odor, no taste, and a melting point of 217—224°C. The hydrochloride is practically insoluble in water and ether. It is freely soluble in chloroform, pyridine, methylacetamide, and mild acid alcohol—water mixtures, and is slightly soluble in dilute acids or alcohol. See Reference 16 for synthesis. 

Phenformin. Phenformin hydrochloride [834-28-6] (1-phenethylbiguanide, A/-(2-phenylethyl)imidodicarbonimidic diamide), is a white to off-white odorless crystalline power having a bitter taste. The melting point is 175—178°C. It is freely soluble in water and alcohol, and practically insoluble in chloroform, ether, and hexane. Its pH in solution is 6.0—7.0. 

Benzophenone. Benzophenone [119-61-9] (diphenyl ketone) exists in a stable form as colorless orthorhombic bisphenoidal prisms when crystallized from alcohol or ether. Other labile forms of lower melting point exist. Benzophenone has been identified as a flavor component of wine grapes and has a geranium-like odor. It is soluble in most organic solvents, and is insoluble in water. 

Cyclic Peroxides. CycHc diperoxides (4) and triperoxides (5) are soHds and the low molecular weight compounds are shock-sensitive and explosive (151). The melting points of some characteristic compounds of this type are given in Table 5. They can be reduced to carbonyl compounds and alcohols with zinc and alkaH, zinc and acetic acid, aluminum amalgam, Grignard reagents, and warm acidified iodides (44,122). They are more difficult to analyze by titration with acidified iodides than the acycHc peroxides and have been sucessfuUy analyzed by gas chromatography (112). 

The principal impurity in potassium metal is sodium. Potassium s purity can be accurately deterrnined by a melting point test (Fig. 2) or atomic absorption if necessary after quenching with alcohol and water. Traces of nonmetallic impurities such as oxygen, carbon, and hydrogen can be deterrnined by various chemical and physical methods (7,8). 

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