In the latter two cases, as in the first, the phosphorus atom, by uniting with an oxygen atom, becomes pentavalently saturated, but at the same time other atoms of oxygen place themselves in between the phosphorus and its directly united hydrogen, forming hydroxyl groups. The alcohol radicals, on the other hand, are so firmly united to the phosphorus that even the strongest nitric acid, at the temperature of the water bath, fails to separate them. The oxidation to phosphoric acid can only be effected at a temperature of about 200° by fuming nitric acid, the alcohol radical being then totally oxidised.

301. The oxides of the tertiary phosphines are obtained with less danger by distilling quatenary phosphonic hydrates:

P(CnH2n+1)4.OH = P(CnH2n+1)30 + CnH2n+29

and by treatment of tertiary phosphines with mercuric oxide: P(CnH2n+1)3 + HgO= P(CnH2n+1)30 + Hg,

than by direct oxidation.

Trimethyl phosphine oxide, P(CH3)30, forms readily soluble crystals, which deliquesce in damp air.

Triethyl phosphine oxide, P(CH)30, crystallises in very deliquescent needles. It melts on heating and boils at 240° without decomposition. Concentrated hydrochloric, hydrobromic, and hydriodic acids convert it into triethyl phosphine dichloride, P(C2H5)3Cl2, dibromide, P(C2H5),Br2, and diiodide, P(C2H3)312, crystalline compounds which can also be obtained by moderated action of the halogens on triethyl phosphine.

Triethyl phosphine oxide gives, with strong acids, salts which are difficult to obtain pure.

Metallic sodium reduces it to triethyl phosphine.

302. The sulphides of the tertiary phosphines, P(CnH2n+1)3S, may be mentioned here. They are crystalline, and are obtained from the tertiary phosphines by direct addition of sulphur, which reacts with considerable evolution of heat.

On bringing sulphur into contact with triethyl phosphine, it melts to a globule, which floats on the liquid and slowly dissolves. When completely saturated with sulphur the liquid solidifies to a crystalline mass of triethyl phosphine sulphide, P.(C2H5)3S, which dissolves pretty readily in boiling water, and separates on cooling in beautiful needles. It is readily soluble in alcohol and ether. It melts at 94°; by boiling with mercuric or plumbic oxide it is converted into triethyl phosphine oxide :

P(C2H5)3S+HgO= HgS + P(C2H5)30;

by sodium it is reduced to triethyl phosphine:

303. The monobasic dialkyl phosphinic acids, P(CnH2n+1)O.OH, are obtained by action of concentrated nitric acid upon secondary phosphonic chlorides. The liquid heats spontaneously to boiling, and evolves chlorine and torrents of nitrous fumes. As soon as the reaction is finished, the excess of nitric acid is removed by repeated evaporation on the water bath with concentrated hydrochloric acid, the latter being finally in great part expelled. The residue is then

dissolved in water and completely freed from hydrochloric acid by shaking with argentic oxide.

To obtain the free acid, the silver is removed from the filtrate by means of hydric sulphide, and after again filtering the liquid evaporated on the water bath.

Dimethyl phosphinic acid, P(CH3)2O.OH, solidifies to a paraffinlike mass, which melts at 76° and can be volatilised unchanged. The silver salt, P(CH3)2O.OAg, prepared by saturation of the acid with argentic oxide, is extremely soluble in water, but is precipitated by strong alcohol in interlaced needles. The baric salt

P(CH3)20.0
P(CH3)20.0 Ba

and the analogous plumbic salt dry to amorphous varnishes, which are readily soluble in alcohol.

By bringing together dimethyl phosphinic acid and phosphonic pentachloride there is formed, according to the equation:

dimethyl oxyphosphine chloride, which distils at 204° and solidifies in crystals on cooling. It melts at 66° and is reconverted by water into the acid:

P(CH3)2O.Cl + HOH = HCl + P(CH3)2O.OH.

Diethyl phosphinic acid, P(C2H3)2O.OH, is left on evaporation as a strongly acid liquid. The argentic salt is also precipitated by alcohol from its aqueous solutions in needles.

304. The dibasic monalkyl phosphinic acids:

P(CnH2n+1)O(OH)2,

result from passing the vapours of primary phosphines into strong nitric acid:

When the violent oxidation has ceased, the liquid is evaporated several times on the water bath, so as to expel nearly all the nitric acid; the aqueous solution then boiled with plumbic oxide, plumbic nitrate remaining dissolved, whilst insoluble plumbic monalkyl CnH2n+1

phosphinate, P

,

>Pb

and some plumbic phosphate separate.

The residue, after washing with water, is heated with acetic acid, which leaves the plumbic phosphate undissolved and converts the neutral monalkyl phosphinate into the soluble acid salt:

The filtrate is decomposed by sulphuretted hydrogen, and after separation of the plumbic sulphide the liquid evaporated until all acetic acid has been expelled.

Methyl phosphinic acid, P(CH3)O(OH)2, forms spermaceti-like crystals, which melt at 105°, partially volatilise unchanged, and are readily soluble in water and alcohol. The solutions react strongly acid. If the acid in presence of water be digested with carbonates, the soluble acid salts are formed; by boiling with metallic oxides or by strongly basic hydrates they are converted into neutral salts of alkaline reaction.

The salts of the alkalies are all difficultly crystallisable.

The acid baric salt Ba(CH3OH) dries to a gummy mass.

O(P.CH3.O.OH)
O(P.CH3.O.OH)

If a pretty concentrated solution of the salt be boiled with plumbic carbonate, and filtered hot, there separates on cooling the acid lead salt Pb (P.CH3.0.OH) in brilliant colourless needles, which by O(P.CH3.0.OH)

washing with pure water are resolved into the free acid and the insoluble, amorphous, neutral salt:

P.CH3.0 (OH)

Pb = P(CH3).O.(OH)2 + P.CH3.

P.CH3.0 (OH)

он

он

Pb.

The acid silver salt, P(CH3).O(OA), which is readily soluble in water in presence of a little free acid, and which crystallises in beautiful needles, behaves similarly with water, being decomposed with separation of the amorphous insoluble neutral silver salt :

P(CH3)O(OAg) 2.

Phosphoric pentachloride converts methyl phosphinic acid into the dichloride of the radical P(CH3)0:

This methyl phosphinic dichloride forms dazzling white crystals, which melt at 32° and boil at 163°. Water reconverts it with explosive violence into the acid:

P(CH3)OCl2 + 2H2O = 2HCl + 2P(CH3)O(OH)2.

Ethyl phosphinic acid, prepared from ethyl phosphine by the same method as the preceding, resembles spermaceti at ordinary temperatures, melts at 44', and though difficult to moisten with water is largely soluble therein. Its salts correspond to those of methyl phosphinic acid.

Other Phosphorus Compounds of the Alcohol Radicals.

305. By action of methylic chloride on phosphide of calcium at high temperatures, diphosphor tetramethyl or phosphor cacodyl (compare cacodyl, § 318), P(CH),, is obtained as a thick oily liquid, which boils at 250° and inflames when exposed to air. Its formation is analogous to that of liquid phosphoretted hydrogen, P,H,, which it corresponds to :

P-Ca

P-Ca

P=(CH3)2
P (CH3)2

+ 4CH2C1 = 2CaCl2 + |

As liquid phosphoretted hydrogen on contact with hydrochloric acid decomposes into the solid and gaseous

5P2H1 = 6CH2 + P ̧H2

so similarly the methyl compound decomposes into trimethyl phosphonic chloride and tetra-phosphor-dimethyl:

5P2(CH3), +6HC1 = 6P(CH3)3HCl + P1(CH3)2

The latter is an amorphous, odourless, and tasteless yellow body.

ARSENIC COMPOUNDS OF THE RADICALS.

306. The compounds of arsenic with the alcohol radicals show some similarities to the nitrogen compounds. The quaternary arsonic salts derived from the strongly basic tetralkyl arsonic hydrates, As(CnH2n+1)4.OH, agree completely in chemical character with the corresponding ammonic compounds.

The tertiary arsines are also known; they are destitute of the distinctly basic properties which the tertiary phosphines possess, but, like these latter, they unite with one atom of oxygen or sulphur or two halogen atoms.

Compounds corresponding to the primary and secondary amines and phosphines are entirely wanting in the arsenic compounds, but compounds of one atom of arsenic united with two alcohol radicals form the mono- or trivalent radical of the so-called cacodyl derivatives, where they are in union with negative elements:

As(CnH2n+1)2Cl and As(CnH2n+1)2Cl3.

In similar manner one alcohol radical united to arsenic appears as a divalent or quadravalent radical:

As(CnH2n+1)Cl2 and As(CnH2n+1)Cl4.

307. The compounds in which arsenic is triad, such as

As(CnH2n+1)3, As(CnH2n+1)2Cl, and As(CnH2n+1)Cl2,

are mostly volatile without decomposition; those in which it is

pentad, such as As(CnH2n+1),Cl, As(CnH2n+1)3C12, As(CnH2n+1)2Cl2, and As(CnH2n+1)Cl, decompose at more or less high temperature, losing one halogen atom and one alcohol radical. This decomposition occurs especially readily with the halogen compounds, and the temperature of decomposition is the lower the fewer alcohol radicals and the more halogen atoms the molecule contains. The alkyl arsenic compounds can therefore, by a series of manipulations, be converted into trivalent inorganic arsenic compounds. Such a series of changes is the following:

As(CnH2n+1),Cl by heating = As(CnH2n+1)3 + CnH2n+1Cl
As(CnH2n+1)3 + Cl2 at ord. temperatures As(CnH2n+1)3Cl2
As(CnH2n+1)3C1, by heating = As(CnH2n+1)2Cl + CnH2n+1Cl
As(CnH2n+1)2C1+ Cl, in the cold As(C,H2n+1)2Cl3

=

As(CnH2n+1)2C1, at 40°-50° = As(CnH2n+1)Cl2 + CnH2n+1Cl As(CnH2n+1)Cl2 + Cl2 in a freezing mixture = As(C,H2n+1)Cl As(CnH2n+1)Cl, even at 0° AsCl3 + CnH2n+1 Cl.

=

All alkyl arsenic compounds-especially the volatile ones--are in the highest degree poisonous, so that their preparation and investigation require extraordinary precautions.

Quaternary Arsonium Compounds.

308. By heating alkylic iodides with sodic or zincic arsenide in apparatus filled with dry carbonic anhydride violent reaction occurs, by which partly cacodyls, As(CnH2n+1), but in larger proportion tertiary arsines, As(CnH2n+1)3, are formed. If the alkylic iodide be employed in excess it forms crystalline quaternary arsonic iodides, according to the equation:

AsNa,+4CnH2n+1I = 3NaI + As(CnH2n+1)4I.

These latter are only separated from the sodic iodide with difficulty; it is more usual, therefore, to avoid excess of the iodide, and to purify the more volatile tertiary arsine from the cacodyl by fractional distillation. It is then mixed with the alkylic iodide, and soon yields at ordinary temperature the arsonic iodide:

As(CnH2n+1)3 + CnH2n+ I = As(CnH2n+1)4I, from which, by shaking its aqueous solution with freshly precipitated argentic oxide, the quaternary arsonic hydrate is obtained:

As(CH2n+1),I + AgOH = AgI + As(CnH2n+1),OH. Mixed quaternary arsonic iodides can be obtained from tertiary arsines and the iodide of another alcohol radical:

As(CH2n+1)3 + CnH2n+ I = As(CnH2n+1)3(CnH2n+1)I; a further group by heating the cacodyls with the iodides of other alcohol radicals:

AS2(CnH2n+1) + 2(CnH2n+1)I = As(C2H2n+1)2I

+ As(CH+1)2(CnH2n+1)2I.

D

The quaternary arsonic hydrates are crystalli-able, very easily