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EXAMPLE 1
Preparation of N-hydroxy-2-pyridinethione
(a) 35g. 2-bromo-pyridine is added to a solution of 38h. perbenzoic acid(20% molar excess) in 600 ml. chloroform, and the solution is allowed to stand for 4 days. the reaction mixture is then extracted three times with 150 ml. portions of 20% hydrochloric acid solution, and the (combined) acid extract is evaporated to dryness in vacuo. the residue (2-bromo-pyridine-N-oxide hydrochloride) is recrystallized from alcohol-ether, yielding about 28g. of the product melting at about 135-136℃.
(b) A solution of 3.3g. 2-bromo-pyridine-N-oxide-hydrochloride in 5 ml. water is heated on a steam bath while a solution of 4.1g. sodium sulfide nonahydrate in 20 ml. water is added in 3 portions at 20-minute intervals. After heating for an additional half hour, the reaction mixture is cooled and acidified to Congo red with 20% hydrochloric acid solution, yielding 1.1g of a solid precipitate melting at 68-70℃. The precipitate is dissolved in 10ml. normal sodium hydroxide solution; and the solution is filtered free of a small amount of sulfur and slowly acidified to Congo red with normal hydrochloric acid solution. The product (N-hydroxy-2-pyridine-thione) is obtained as colorless crystals melting at about 68℃. in a yield of about 0.68g.

EXAM PLE 2
Preparation of N-hydroxy-3-ethoxy-2-pyridinethione

(a) A solution of 28g. 2-bromo-3-ethoxy-pyridine hydrobromide in 200 ml. Water is made strongly alkaline by addition of 40% potassium hydroxide solution,and the free base formed is extracted three times with 150 ml. Portions of chloroform. The (combined) chloroform solution is dried, and added to a solution of 16.6g. perbenzoic acid in 300ml.chloroform;and the reaction mixture is allowed to stand at room temperature for 3 days, and the extracted three times with 150ml.portions of 20% hydrochloric acid solution. The (combined) aqueous extract is concentrated to dryness under reduced pressure,yielding about 13g. of 2-brom-3-ethoxy-pyridine-N-oxide hydrochloride melting at about 158-160°C.On recrystallization from ether,the melting point of the product is raised .The (combined) aqueous extract is concentrated to dryness under reduced pressure,yielding about 13g ed to about 159-160°C.
(b) A solution of 30 g. 2-bromo-3-ethoxy-pyridine-N-oxide hydrochloride in 200 ml. water is neutralized with 25% sodium hydroxide solution; and to this solution is added a solution of 20 g. of sodium hydrosulfide in 100 ml. Water While heating on a steam bath. The reaction mixture is heated for 1 hour, and filtered; the filtrate is cooled and solution;to Congo red with 20% hydrochloric acid solution; and the crystals formed (N-hydroxy-3-ethoxy-2-pyridinethione) are recovered by filtration. About 19g.of the product is obtained,melting at about 97-100°C On recrystallization from aqueous alcohol. About 17.5g. of a product melting at about 101-103°C is obtained

EXAM PLE 3
Preparation of N-hydroxy-5-bromo-2-pyridine-thione
(a) A solution of 21.2g. 2,5-dibromo-pyridine in 50 ml. chloroform is added to a solution of 15.6g perbenzoic acid in 270 ml. chloroform. After standing 4 days at room temperature, the reaction mixture is extracted three times with 200 ml. portions of 20% hydrochloric acid solution; and the (combined)aqueous extract is concentrated to dryness, yielding about 4.5g. of 2,5-dibromo-pyridine-N-oxide hydrochloride melting at about 161-162℃. On recrystallization from absolute alcohol, the melting point of the product is raised to about 165-166℃.
(b) A solution of 3.35g 2.5-dibromo-pyridine-N-oxide hydrochloride in 25 ml. water is neutralized with 25% sodium hydroxide solution; and a solution of 3g. sodium hydrosulflde(70%) in 50 ml. water is added, and the reaction mixture is heated for 1 hour on a steam bath. The reaction mixture is them filtered and cooled; the filtrate is acidified to Congo red with 10% hydrochloric acid solution; and the precipitate (N-hydroxy-5-bromo-2-pyridinethione) is recovered. The product, obtained in a yield of about 1 g. melts at about 120-123℃; and on recrystallization from aqueous alcohol, about 600 ml. of a product melting at about 130-131℃. is obtained.

EXAM PLE 4
Preparation of N-hydroxy-3-methyl-2-pyridine-thione
(a)A solution of 37.8 g 2-bromo-3-methyl-pyridine in 50 ml. Chloroform is added to solution of 39.4 g. perbenzoic acid in 1300ml. Chloroform. After standing at room temperature for 3 days,the reaction mixture is extracted three time with 300 ml. Portions of 20% hydrochloric acid solution; and the (combined) aqueous extract, yielding about 33 g. 2-bromo-3-methyl-pyridine-N-oxide hydrochloride,melting at about 177-179°. With decomposition. On recrystallization from absolute alcohol, the product melts at about 179-180°. With decomposition.
A solution of 8.5 g . 2-bromo-3-methyl-pyridine-N-oxide hydrochloride in 50 ml. Water is neutralized with 25% sodium hydroxide solution , and a solution of 7 g. sodium hydrosulfide (70%) in 50 ml. Water is added thereto, and the reaction mixture is heated for an hour on a steam bath. The reaction mixture is then filtered and cooled; and the filtrate is acidified to Congo red with 20% hydrochloric acid solution, yielding about 2.8 g. N-hydroxy-3-methyl-2-pyridine-thione melting at about 71-73°. On recrystallization from aqueous alcohol, the product melts at about 74-75°

EXAM PLE 5
prevention of N-hydroxy-4-methyl-2-pyridine-thione
(a) A solution of 20.8g. 2-bromo-4-methyl-pyridine in 50 ml. chloroform is added to a solution of 23g. perbenzoic acid in 4ooml, chloroform, and the reaction mixture is allowed to stand at room temperature for 3 days. The solution is then extracted three times with 100ml. portions of 20% hydrochloric acid solution and the (combined) acid extract is concentrated to dryness under reduced pressure, yielding about 22g. 2-bromo-4-methyl-pyridine-N-oxide hydrochloride melting at about 138-141℃. On recrystallization from absolute alcohol, about 16.5g of a product melting at about 147-148℃. is obtained.
(b) A solution of 16.5g. 2-bromo-4-methyl-pyridine-N-oxide hydrochloride in 30 ml. water is neutralized with 25% sodium hydroxide solution, and a solution of 11.8g. sodium hydrosulfide(70%) in 30 ml. water is added thereto portionwise. The reaction mixture is then heated for an hour on a steam bath, filtered, and cooled; and the filtrate is acidified to Congo red with 20% hydrochloric acid solution, yielding about 6g N-hydroxy-4-methyl-2-pyridinethione melting at about 59-61℃. On recrystallization from aqueous alcohol, about 3g. of a product melting at about 62-63℃. is obtained.

EXAM PLE 7

Preparation of N-hydroxy-6-methyl-2-pyridine-thione
（A）A solution of 43 g. 2-bromo-6-methy-pyridine in 100ml.chloroform is added to a solution of 42 g. perbenzoic acid in 625 ml. Chloroform, and the reaction mixture is allowed to stand at room temperature for 3 days. The reaction mixture is the extracted three times with 300 ml. Portions of 20% hydrochloric acid solution; and the (combined) acid extract is concentrated to dryness under reduced pressure, yielding about 34 g. 2-bromo-6-methyl-pyridine-N-oxide hydrochloride melting at about 185-186°with decomposition. On recrystallization from absolute alcohol, the product melts at about 185-186°
(B) A solution of 21 g. 2-bromo-6-methyl-pyridine-N-oxide hydrochloride in 150 ml. Water is neutralized with 25% aqueous sodium hydroxid solution;and a solution of 15g. sodium hydrosulfide(70%) in 100 ml,water is added thereto, and the reaction mixture is heated for an hour on a steam bath. The reaction mixture is heated for an hour on a steam bath. The reaction mixture is the filtered, and cooled; and the filtrate is acidified to Congo red with 20% hydrochloric acid solution,yielding about 6.1g. N-hydroxy-6-methyl-2-pyridinethione melting at about 51-54℃. On recrystallization from aqueous alcohol, the product melts at about 52-54℃.

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