The majority of non-metals also react directly on chlorine; hot sulphur and phosphorus burn in it and combine with it at the ordinary temperature. Only nitrogen, carbon, and oxygen do not combine directly with it. The chlorine compounds formed by the non-metals—for instance, phosphorus trichloride, PCl3, and sulphurous chloride, &c., do not have the properties of salts, and, as we shall afterwards see more fully, correspond to acid anhydrides and acids; for example, PCl3—to phosphorous acid, P(OH)3:
| NaCl | FeCl 2 | SnCl 4 | PCl 3 | HCl |
|---|---|---|---|---|
| Na(HO) | Fe(HO) 2 | Sn(HO) 4 | P(HO) 3 | H(HO) |
As the above-mentioned relation in composition—i.e. substitution of Cl by the aqueous residue—exists between many chlorine compounds and their corresponding hydrates, and as furthermore some (acid) hydrates are obtained from chlorine compounds by the action of water, for instance,
| PCl 3 | + | 3H 2 O | = | P(HO) 3 | + | 3HCl |
|---|---|---|---|---|---|---|
| Phosphorus trichloride | Water | Phosphorus acid | Hydrochloric acid |
whilst other chlorine compounds are formed from hydroxides and hydrochloric acid, with the liberation of water, for example,
NaHO + HCl = NaCl + H2O
we endeavour to express this intimate connection between the hydrates and chlorine compounds by calling the latter chloranhydrides. In general terms, if the hydrate be basic, then,
| M(HO) | + | HCl | = | MCl | + | H 2 O |
|---|---|---|---|---|---|---|
| hydrate | hydrochloric acid | chloranhydride | water |
and if the hydrate ROH be acid, then,
| RCl | + | H 2 O | = | R(HO) | + | HCl |
|---|---|---|---|---|---|---|
| Chloranhydride | water | hydrate | hydrochloric acid |
The chloranhydrides MCl corresponding to the bases are evidently metallic chlorides or salts corresponding to HCl. In this manner a distinct equivalency is marked between the compounds of chlorine and the so-called hydroxyl radicle (HO), which is also expressed in the analogy existing between chlorine, Cl2, and hydrogen peroxide, (HO)2.
As regards the chloranhydrides corresponding to acids and non-metals, they bear but little resemblance to metallic salts. They are nearly all volatile, and have a powerful suffocating smell which irritates the eyes and respiratory organs. They react on water like many anhydrides of the acids, with the evolution of heat and liberation of hydrochloric acid, forming acid hydrates. For this reason they cannot usually be obtained from hydrates—that is, acids—by the action of hydrochloric acid, as in that case water would be formed together with them, and water decomposes them, converting them into hydrates. There are many intermediate chlorine compounds between true saline metallic chlorides like sodium chloride and true acid chloranhydrides, just as there are all kinds of transitions between bases and acids. Acid chloranhydrides are not only obtained from chlorine and non-metals, but also from many lower oxides, by the aid of chlorine. Thus, for example, CO, NO, NO 2 , SO 2 , and other lower oxides which are capable of combining with oxygen may also combine with a corresponding quantity of chlorine. Thus COCl 2 , NOCl, NO 2 Cl, SO 2 Cl 2 ,