The general nature of xanthate

Yellow medicine is a pale yellow powder, hence the name. Soluble in water, depending on the specific conditions of the plant, it can be used as a 1-10% aqueous solution. The dosage is generally 50-150 g / ton. The following properties of xanthate are worth noting.

1. Dissociation, hydrolysis and decomposition The xanthate is a sodium or potassium salt of xanthogen , which has a high solubility in water. And ionization occurs; xanthate is a weak acid salt, which is easily hydrolyzed in water to form part of xanthogen, which is easily decomposed in an acidic medium. The reaction of disintegration, hydrolysis and decomposition of xanthate in water can be expressed by the following reaction formula:

ROCSSNa=ROCSS ^- +Na ⁺ xanthate ionization

ROCSS ^- +H ₂ O ←→ROCSSH+OH ^- Xanthate hydrolysis

ROCSSH→CS ₂ +ROH xanthogen decomposition

ROCSSH←→ROCSS ^- +H ⁺ xanthogen ionization

The negative logarithm (PKa) and decomposition constants for some xanthogen ionization constants are listed in Table 1. It can be seen from the table 1 that xanthogen is a relatively weak acid with a PKa value of 2 to 3, so the xanthate has a hydrolysis effect. From the viewpoint of the decomposition constant, in general, the larger the molecular weight, the smaller the decomposition constant in the aqueous solution. In other words, the more molecular weight of xanthogen, the more stable the aqueous solution.

It is generally believed that when pH < 7, xanthate is hydrolyzed to xanthogen, and the resulting xanthogen is further decomposed into alcohol and carbon disulfide.

2. Oxidation At pH = 7 to 12, xanthate is oxidized to dihuang in an aqueous solution.

The pKa value and decomposition constant of several xanthogens

Xanthogen name	Xanthogen structure	pKa value	Decomposition constant	Solvent
Methionine Ethyl xanthate Isopropyl xanthate Butyl xanthate Amyl xanthate Isoamyl xanthate Methionine Ethyl xanthate Isopropyl xanthate Butyl xanthate Amyl xanthate Isoamyl xanthate Thioglycolic acid		2.29 2.74 2.16 3.03 2.96 2.85 2.57 3.03 5.18 2.16 2.40 2.95 2.17	0.024 0.033 0.027 0.018 0.011 0.012 0.903 0.689 0.396 0.863 0.699 0.616 0.643	water water water water water water dimethylformamide

    Shuanghuang is also a sulphide ore collector, and its selectivity is better than that of xanthate. [next]

3. When PH=7～12, xanthate is directly decomposed in aqueous solution. It is generally considered that when PH value is less than 7, xanthate is decomposed into alcohol and carbon disulfide. When PH=7～12, oxygen dissolved in water is oxidized to double. Xanthate; some people think that this is not comprehensive, in addition to the above reaction, there is a decomposition reaction as shown in Figure 1;

In Figure 1, dithiocarbonate The hydrolysis is carried out, the hydrolyzate is unstable, and soon becomes the final product carbonate, bicarbonate, HS ^- root, trithiocarbonate. Because of the rapid reaction, the presence of these intermediates cannot be determined chemically; However, in turn, using any of these intermediate products and alcohol, a small amount of xanthate can be obtained. This fully proves the existence of balance.

In addition, the sea ultraviolet spectrum curve of xanthate was measured as shown in FIG. The curve A in Fig. 2 is measured at pH = 10 to 11, the first absorption peak is 2180 to 2220 A, and the second absorption peak is 2800 to 2900 A; the curve B is a newly formulated ethyl-sulfurized potassium carbonate. The ultraviolet spectrum of the solution, which is unstable, has a half-life of about 10 hours at pH = 8. Comparing the two curves of A and B, it can be considered that the sulfided carbonate is the decomposition of ethyl potassium xanthate because both curves have the largest absorption peak at 2220A. The absorption peak at 2800 to 2900A is a double xanthate. At pH=6～7, the ultraviolet spectrum data of xanthate was measured, and the xanthate solution was placed with a buckle of about half-life, and the only reaction product was CS ₂ . From the ultraviolet spectral curve, it is further proved that the decomposition process of Figure 1 is culturally present.

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4, the situation of xanthate in strong acidic medium, xanthate in the strong acidic medium, in addition to decomposition to produce alcohol and carbon disulfide, there is also the presence of proton-bound xanthogen in the solution, the balance of xanthate in strong acidic medium The status can be expressed by:

H ⁺ +ROCSS ^- ←→ROCSSH

H ⁺ +ROCSSH ←→ROSSH ₂ ⁺ (xanthogen combined with protons)

ROCSSH ←→ROH+CS ²

The ratio of ROCSS ^- , ROCSSH and ROCSSH ₂ ⁺ in solution was determined spectrophotometrically at different hydrogen ion activities. The results are shown in Table 2.

ROCSSH, ROCSSH ₂ ⁺ ratio of the three Table 2

HCl concentration (M)	Relative percentage (%)
	ROCSS -	ROCSSH	ROCSSH 2 +
0.47 1.01 1.99 3.01 4.02 5.00	8.78 3.37 0.94 0.29 0.09 0.03	85.58 84.64 77.45 70.11 63.85 58.76	5.64 11.99 21.61 29.60 36.02 41.24

However, the formation of alcohol and carbon disulfide in a strongly acidic medium is reversible. The decomposition of xanthate accounts for the dominant aspect of reversible anti-Qing, so most of the xanthate is decomposed in a short period of time.

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