Petroleum Ether Compounds

If the substance is found to be far too soluble in one solvent and much too insoluble in another solvent to allow of satisfactory recrystallisation, mixed solvents or solvent pairs may frequently be used with excellent results. The two solvents must, of course, be completely miscible. Recrystallisation from mixed solvents is carried out near the boiling point of the solvent. The compound is dissolved in the solvent in which it is very soluble, and the hot solvent, in which the substance is only sparingly soluble, is added cautiously until a slight turbidity is produced. The turbidity is then just cleared by the addition of a small quantity of the first solvent and the mixture is allowed to cool to room temperature crystals will separate. Pairs of liquids which may be used include alcohol and water alcohol and benzene benzene and petroleum ether acetone and petroleum ether glacial acetic acid and water. 

The alcohol may be purified by conversion into the calcium chloride addition compound. Treat it with anhydrous calcium chloride much heat is evolved and the addition compound is formed. After several hours, remove any oil which has not reacted by washing with petroleum ether (b.p. 60-80°). Decompose the solid with ice water, separate the alcohol, dry and distil. 

Amino-4,6-dichlorophenol. This compound (11) forms long white needles from carbon disulfide, and aggregate spheres from benzene. It sublimes at 70—80°C (8 Pa = 0.06 mm Hg) and decomposes above 109 °C. It is freely soluble in benzene and carbon disulfide, and is sparingly soluble in petroleum ether, water, and ethanol. The free base is unstable and the hydrochloride salt (mp 280—285°C, dec) is employed commercially. 

Hydroxyacetanilide. This derivative (21), also known as 4-acetamidophenol, acetaminophen, or paracetamol, forms large white monoclinic prisms from water. The compound is odorless and has a bitter taste. 4-Hydroxyacetani1 ide is insoluble in petroleum ether, pentane, and ben2ene slightly soluble in diethyl ether and cold water and soluble in hot water, alcohols, dimethylformamide, 1,2-dichloroethane, acetone, and ethyl acetate. The dissociation constant, pfC, is 9.5 (25°C). 

Alkylation and arylation of organosilanes occur readily with alkyl and aryl alkaU metal compounds. Yields from these reactions are good but are iafluenced by steric requirements on both silane and metal compounds. There is Httie iaductive effect by the organic groups attached to siUcon, as measured by the yield of products (126,127). These reactions proceed more readily ia tetrahydrofuran and ethyl ether than ia ligroin or petroleum ether, where R and are alkyl or aryl and M is Li, Na, or K. 

Aromatic hydrocarbons can be purified as their picrates using the procedures described for amines. Instead of picric acid, 1,3,5-trinitrobenzene or 2,4,7-trinitrofluorenone can also be used. In all these cases, following recrystallisation, the hydrocarbon can be isolated either as described for amines or by passing a solution of the adduct through an activated alumina column and eluting with toluene or petroleum ether. The picric acid and nitro compounds are more strongly adsorbed on the column. 

These substances contain the -C=NH group and, because they are strong, unstable bases, they are kept as their more stable salts, such as the hydrochlorides. (The free base usually hydrolyses to the corresponding oxo compound and ammonia.) Like amine hydrochlorides, the salts are purified by solution in alcohol containing a few drops of hydrochloric acid. After treatment with charcoal, and filtering, dry diethyl ether (or petroleum ether if ethanol is used) is added until crystallisation sets in. The salts are dried and kept in a vacuum desiccator. 

Ketones are more stable to oxidation than aldehydes and can be purified from oxidisable impurities by refluxing with potassium permanganate until the colour persists, followed by shaking with sodium carbonate (to remove acidic impurities) and distilling. Traces of water can be removed with type 4A Linde molecular sieves. Ketones which are solids can be purified by crystallisation from alcohol, toluene, or petroleum ether, and are usually sufficiently volatile for sublimation in vacuum. Ketones can be further purified via their bisulfite, semicarbazone or oxime derivatives (vide supra). The bisulfite addition compounds are formed only by aldehydes and methyl ketones but they are readily hydrolysed in dilute acid or alkali. 

Successful recrystallization of an impure solid is usually a function of solvent selection. The ideal solvent, of course, dissolves a large amount of the compound at the boiling point but very little at a lower temperature. Such a solvent or solvent mixture must exist (one feels) for the compound at hand, but its identification may necessitate a laborious trial and error search. Solvent polarity and boiling point are probably the most important factors in selection. Benzhydrol, for example, is only slightly soluble in 30-60 petroleum ether at the boiling point but readily dissolves in 60-90° petroleum ether at the boiling point. 

Camphene forms a well-defined nitrite, and a nitroso-nitrite, when treated in the following manner A well-cooled solution of camphene in petroleum ether is mixed with a saturated solution of sodium nitrite, and dilute acetic acid is added. The mixture is well stirred, being kept cool all the time. Camphene nitrosonitrite, CuHi NjOj, separates and on recrystallisation forms crystals which decompose at about 149°. The petroleum ether solution, which has been filtered off from this compound, is shaken with a concentrated solution of pK)tassium hydroxide, which removes camphene nitrosite, CjQHigNjOj, in the form of its potassium salt. When this is decomposed with acids it yields the free nitrosite. This compound is a greenish oil, with a pleasant odour, easily decomposing when heated to 50°. 

Caryophyllene nitrosite is an interesting compound. It has the formula CJ5H24N2O3, and was first produced by Schreiner and Kremers. It is form by treating a mixture of equal volumes of the sesquiterpene and petroleum ether with a concentrated solution of sodium nitrite and glacial acetic acid. It crystallises in fine blue needles when re-crvstallised from alcohol it melts at 115° and has a specific rotation -h 103°. 

By treating this blue nitrosite, which Deussen calls )3-caryophyllene nitrosite, with alcoholic potash at 0°, it is converted to a colourless isomer, melting at 139°, which Deussen terms )3-caryophyllene isonitrosite. By treatment with boiling petroleum ether decomposition takes place and a compound melting at 159° is formed, of formula not yet established, and a nitro-compound of the formula Cj5H22N204, melting at 130 5°. 

For the identification of citronellal, the semi-carbazone is the easiest cry stalline compound to prepare. It results if an alcoholic solution of citronellal be well-shaken with a solution of semi-carbazide hydrochloride and acetate of sodium. It is purified by recrystallisation from a mixture of chloroform and petroleum ether, and then melts at 84°. It also forms a well-defined naphthocinchoninic acid, which is prepared in the same manner as the corresponding citral compound. It melts at 225°. 

Thujone is best identified by its tribromo-compound, CjflHjgBrgO, melting at 121° to 122°. It is obtained by adding 5 c.c. of bromine (at once) to a solution of 5 grams of thujone in 30 c.c. of petroleum ether. The tribromo-compound separates on evaporation of the solvent and is washed with alcohol and recrystallised from boiling acetic ether. 

Bayer and Henrich have prepared a bisnitrosopulegone, which is very useful for the identification of the ketone. A solution of 2 c.c. of pulegone in 2 c.c. of petroleum ether is cooled in a freezing mixture and 1 c.c. of amyl nitrite and a trace of hydrochloric acid are added. Fine needles of the bisnitroso compound quickly separate, which, when dried on a porous plate and washed with petroleum ether, melt at 81 5°. 

In judging whether or not petroleum ether should be added, the following rule should be observed Add enough petroleum ether to soften the cineol arsenate, so as to obtain a plastic mass the quantity necessary never exceeds 5 c.c., and decreases vsith oils containing less than 80 per cent, of cineol. The object of adding petroleum ether is merely to soften the hard mass and to aid in the separation of non-cineol constituents of the oil a large excess of petroleum ether will decompose the compound. 

Damascenine, CjqHj3N03, is a nitrogenous compound of an alkaloidal nature, which is present in the oil of Nigella damascena to the extent of about 9 per cent. It can be extracted from the oil by shaking it with dilute hydrochloric acid, rendering the aqueous liquid alkaline and extracting the alkaline liquid with petroleum ether. 

Indol can be isolated from, and determined in, essential oils in the following manner Ihe oil is mixed with 10 per cent, of picric acid and heated to 60°. Excess of petroleum ether is then added. A picric acid compound of indol separates in long red crystals, which are washed with petroleum ether and decomposed by caustic alkali, and the free indol extracted by ether, and the residue left on evaporation of the ether steam-distilled, when pure indol passes over. 

The solid material Is separated by filtration and the chloroform solution concentrated to an oil under reduced pressure. The oil is dissolved in 50 ml of trichloroethylene, the solution treated with charcoal, filtered and the filtrate added to 125 ml of hexane. The crystalline material which forms on standing at refrigerator temperature is removed by filtration, washed with light petroleum ether and dried at about 50°C. Approximately 20 g of product are obtained. On recrystaliizing from trichloroethylene-hexane, 17.8 g of purified compound are obtained, (VIP 89° to 91°C. 

This compound is obtained by heating a mixture of 1,1 -dimethylol cyclopentane and phenyl isocyanate at a temperature of B5°C to90°Cfor one-half hour. The resultant product is washed with petroleum ether, recrystallized from methanol, dissolved in acetone (impurities are filtered off) and recrystallized from acetone. 

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