readily soluble in alcohol and water. By strong bases they are converted into carbonates, ammonia, and alcohols : -NH2 +NH, + +2KOH= CO(OK)2 + NH3 + HO.CnH2n+1; and by heating with excess of alcoholic ammonia, yield urea and alcohols : which melt at 55° and boil at 177°. Ethylic carbamate, CO. (NH)(O.C,H,), crystallises in glittering leaves, which melt below 100° and boil at about 180°. Propylic carbamate, CO(NH2)(O.CH2.CH2.CH3), large colourless prisms, which melt at 50° and are less soluble in water than in alcohol or ether, needles, melting at 66° and boiling at 220°. 232. The alkylic allophanates stand in the same relation to biuret (§ 137) as the carbamates to urea : A general method of preparation consists in passing cyanic acid vapour into alcohols : They are easily obtained by heating alkylic chlor-carbonates with and also, together with carbamates, by the action of high-boiling alcohols upon urea at higher temperatures; e.g. As they are more difficultly soluble in water than the carbamates formed at the same time (§ 231), they can be readily separated from the latter. On submitting alkylic allophanates to dry distillation, they evolve alcohols, and leave a residue of cyanuric acid, which on further heating is resolved into cyanic acid: 3NH2.CO.NH.CO.O.CnH2n+1 = 3HO.CnH2n+1 +2C303N3H3. On heating them in closed tubes at 100° with alcoholic ammonia, they yield biuret: NH,.CO.NH.CO.O.CnH2n+1 + NH,=NH,.CO.NH.CONH, + HO.CnH2n+1 233. Methylic, ethylic, and isoamylic allophanates have been prepared; the two first crystallise in needles, the last in nacreous plates melting at 162°. If the alkylic allophanates are rubbed together with baric hydrate in the cold, baric allophanate is formed, together with alcohol: 2(C,H.O.CO.NH.CO.NH,) + Ba(OH), Ba(O.CO.NH.CO.NH,), +2C2H,.OH. = Baric allophanate, however, is very readily decomposed, and allophanic acid cannot be obtained by addition of strong acids, as it splits up into carbonic anhydride and urea : NH,.CONH.CO.O Ba + 2HCl = BaCl2 + CO2 + 2(NH2.CO.NH2). Compounds of Alcohol Radicals with the Cyanogen Acids. 234. The true alkylic cyanates are very unstable liquids, insoluble in water, and are formed when the vapour of cyanogen chloride is passed into alcoholic solutions of metallic alkylate at a low tempera ture: CEN + NaO.CH3 = NaCl + CEN methylic cyanate. CEN+NaO.C2H, NaCl + CEN ethylic cyanate. Cl = O.C2H5 With alkalies they yield alcohol and a metallic cyanate: CEN O.CnH2n+1 + KOH = CEN + CnH2n+1.OH. OK The pseudocyanates are isomeric with the cyanates, and for a long time were mistaken for them. These, however, belong to the nitrogen compounds of the alcohol radicals, and will be considered later. 235. During their formation even, the alkylic cyanates partly polymerise, but completely on long standing, yielding thereby the solid, crystalline, alkylic true cyanurates. This change occurs especially easily with the methyl compound. Methylic cyanurate, C2Ñ¿(O.CH3)3, or CH3.O.C-N N-C-O.CH3 CH3.O.C-N crystallises in colourless needles, easily soluble in ether, which melts at 134° and boils at 160°-170°. The distillate solidifies to a crystalline mass, which consists, however, of the isomeric methylic pseudocyanurate, which crystallises in thick prisms, melts at 175°, and will be further described amongst the nitrogen compounds of the alcohol radicals (§ 281). Methylic cyanurate yields, on boiling with potassic hydrate, methylic alcohol and potassic cyanurate; by heating with ammonia it is converted into Methylic ammelide, or methylic amido-cyanurate: NH2 (C3N3) O.CH3 + NH3 HO.CH3 + (C3N3)O.CH, O.CH3 = forming rhombic tables, melting at 212°, difficultly soluble in cold water and in ether, more readily in boiling water and in ethylic alcohol. SULPHUR COMPOUNDS OF THE ALCOHOL RADICALS. 236. As far as is known the sulphides of the elements correspond to the oxides in their general chemical properties; this agreement of sulphur with oxygen also occurs in organic compounds, so that all organic sulphides containing dyad sulphur show very complete analogy to the oxygen compounds of corresponding composition. The mercaptans, or thio-alcohols, CnH2n+1.SH, correspond to the alcohols; the thio-ethers, or alcoholic sulphides, (CnH2n+1)2S, to the ethers. In many cases the sulphur developes its higher valency, forming bodies without analogy among the mineral compounds of sulphur. Mercaptans, or Thio-alcohols, CnH2n+1.SH. 237. The alkylic sulphhydrates, or thio-alcohols, can be prepared from many of the derivatives of the alcohol radicals already mentioned. The alcohols are partly converted into the mercaptans when heated with phosphoric pentasulphide. In a similar manner to its decomposition by water into phosphoric acid and hydric sulphide, it gives, in part, with alcohols, phosphoric acid and thio-alcohols. The phosphoric acid is, at the same time, in considerable part converted into its alkylic salts, so that the main reaction may be represented by the equation: P2S5 + 8(CnH2n+1.OH) = (CnH2n+1)2HPO4 + (CnH2n+1)H2PO4 +5CH 2n+1.SH. But as phosphoric pentasulphide behaves to the thio-alcohols similarly to P2O on the alcohols, alcoholic thio-phosphates are also formed. From the haloid compounds of the alcohol radicals the mercaptans can be produced by heating with alcoholic solution of potassic sulphhydrate: CnH2n+1Cl+KSH = CnH2n+1.SH + KCl. A portion of the mercaptan first formed reacts on some still unchanged potassic sulphhydrate, forming the potassic thio-alkylate (compare $ 197): CnH2n+1.SH + KSH = SH2 + CnH2n+1∙S.K ; 2 which in its turn reacting on the alkylic haloid compound, gives rise to the formation of thio-ethers: CnH2n+1.SK + CnH2n+1Cl = (CnH2n+1)2S+ KCl. It is therefore generally preferable to submit a mixture of an alkylic potassic sulphate with potassic sulphhydrate to distillation: (CnH2n+1)KSO4 + KSH = K2SO1 + CnH2n+1.SH. 238. The thio-alcohols are mostly liquids of most unpleasant garlic odour, which distil without decomposition and are nearly insoluble in water. Their sulphhydroxylic hydrogen atom is more easily replaced by metals than the hydroxylic hydrogen of alcohols, being not merely the case only by the alkalies, but also with equal or greater ease by those heavy metals which are precipitated from acid solutions by hydric sulphide. This reaction occurs with especial ease with mercury. On shaking an alcoholic solution of a thio-alcohol with mercuric oxide, a crystalline mercuric thio-alcoholate is formed, with considerable evolution of heat: 2CnH2n+1.SH + Hg0 = H20 + CnH2n+1-S whilst with an alcoholic solution of mercuric chloride a precipitate of the difficultly soluble chlor-mercuric thio-alkylate is obtained: CnH2n+¡.SH+ HgCl2 = HCl + CnH2n+1.S-Hg-Cl. From these reactions the thio-alcohols have got the name mercaptans (from mercurio-aptum); the metallic derivatives are frequently termed mercaptides. All oxidating bodies react very readily on the mercaptans, the more energetic, such as concentrated nitric acid, often with great violence. By such oxidation the sulphur is not separated from the carbon, but by taking up three atoms of oxygen is converted into the group SO.OH, which, united to the alcohol radical, forms a sulphonic acid : CnH2n+1.SH + 2HNO3 = H2O + N2O2+ CnH2n+ .S O 239. Methylic mercaptan, or methylic thio-alcohol, CH3.SH, is a mobile liquid which floats on water, boils at 20°, and yields with mercuric oxide shining colourless plates of mercuric sulph-methylate: CH3.S CH.S Hg. Ethylic mercaptan, or ethylic thio-alcohol, C2H,.SH, is a colourless mobile liquid, of sp. gr. 835 and boiling at 36°. By quick evaporation in the air, e.g. a drop at the end of a glass rod, it absorbs heat so rapidly that a portion solidifies in crystalline leaves. Mercuric ethylic CH.S mercaptide, or mercuric sulph-ethylate, CH,SHg, crystallises from C2H.S boiling alcohol in beautiful silvery plates, which melt at 86°. By hydric sulphide it is decomposed with re-formation of mercaptan : (C2H,,S)2Hg + H2S = HgS + 2C2H SH, and serves for the purification of the latter. Aurous thio-ethylate, C2H5.S.Au, is precipitated, on mixing dilute alcoholic solutions of mercaptan and auric chloride, as a white soft mass. Potassic thio-ethylate, usually prepared by dissolving potassium in mercaptan : 5 2C,H,.SH+K2 = H2 + 2C,H.SK, crystallises in colourless needles. Propylic thio-alcohol, CH3-CH2-CH2.SH, boils at 67°-68°. CH3 CHCH.SH, boils between 57° and 60o. Isopropylic thio-alcohol, CH Butylic thio-alcohol, CH3.CH2.CH2.CH2.SH, boils at 98°. Isoamylic thio-alcohol, CH3CH.CH.CH..SH, is a colourless oil of sp. gr. 855 at 0° and boiling at 120°. Thio-ethers, or Sulphides of the Alcohol Radicals, (CH2n+1)2S. 240. One method of formation of these bodies has been already given (§ 237). They are obtained in nearly theoretical quantity by 1 |