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As mentioned above, the black medicine is obtained by the action of alcohol or phenol and phosphorus pentasulfide . The reaction is as follows:
S
/
P 2 S 5 + 4ROH—→2(RO) 2 P—SH+H 2 S
Alcohol or phenol black medicine
But the following reactions will also occur simultaneously:
S
/
P 2 S 5 + 2ROH —→(RO) 2 —P—SH+HPS 3
Alcohol or phenol
S
/
HPS 3 +2ROH —→ (RO) 2 —P—SH+H 2 S
When the reaction temperature is too high, the two-molecule acid black medicine will remove one molecule of H 2 S, and become a thiophosphoric anhydride derivative. For example, when the cresol black medicine is at 150 ° C or higher, the hydrogen sulfide will be dehydrated as follows:
When the temperature reaches 250 to 300 ° C, it will be decomposed into thiophenol. Therefore, when manufacturing black medicine, it is necessary to take appropriate reaction conditions depending on the type of black medicine produced.
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