Question: the conversion of a thiol into a disulfide occurs by what type of chemical reaction
[{'answer': 'coupling of two thiol groups', 'provenance': [{'wikipedia_id': '65948', 'title': 'Disulfide', 'start_paragraph_id': 1, 'start_character': 184, 'end_paragraph_id': 1, 'end_character': 212, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '65948', 'title': 'Disulfide', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 533, 'bleu_score': 0.6271408403867851, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 10334726792195273499}, 'section': 'Section::::Abstract.'}]}]