Results and Discussion the 4-Bromophenacyl Esters 6 (Table VII)

A Convenient Preparation of Anhydrous Alkali Metal Thiocarboxylates

Shinzi Kato*, Motohiro Oguri, and Masaru Ishida Department of Chemistry, Faculty of Engineering, Gifu University, Yanagido, Gifu 501-11, Japan Z. Naturforsch. 38b, 1585-1590 (1983); received July 5, 1983 Lithium Thiocarboxylates, Sodium Thiocarboxylates, Potassium Thiocarboxylates, Rubidium Thiocarboxylates, Caesium Thiocarboxylates A series of alkali metal thiocarboxylates (1-5) were found to be readily obtained in high yields by the reaction of thiocar boxy lie acids with metal hydrides (LiH, NaH, KH), and rubidium or caesium acetates, respectively. Their physical properties were disclosed.

Alkali metal salts of thiocarboxylic acid, especially lithium thiocarboxylates (la-e), sodium 2- cially anhydrous salts, are of the most important methyl- (2c), 3-methyl- (2d), and 2-chlorothio- starting materials. However, only a limited amount benzoates (2f), and rubidium 2-methylthiobenzoate of information on their preparation and spectral (4 c) are too strong hygroscopic (deliquescent) to data has been available because of their strong carry out their microanalyses. The lithium salts (1) hygroscopicity [1]. Recently, the convenient prep- are soluble in ether, but less soluble in chloroform. aration methods of a series of anhydrous alkali Surprisingly, alkali metal thiocarboxylates except metal dithiocarboxylates were developed [2]. This the lithium salts (1), especially in an anhydrous result stimulated us to develop similar convenient solid state, show very strong static electrical prop- methods for the preparation of anhydrous alkali erties. This is in sharp contrast to alkali metal metal thiocarboxylates and to compare their phys- carboxylates, which do not show such a property. ical properties. The structures of 1, 2, 3, 4, and 5 obtained here were established by IR and UV spectral data, and elemental analysis (Table VI), or by conversion to Results and Discussion the 4-bromophenacyl esters 6 (Table VII). Preparation For the preparation of lithium (1), sodium (2), IR spectra and potassium thiocarboxylates (3), the reactions As shown in Tables I-V, the vasC=0 vibrations of of thio acids with lithium-, sodium-, and potassium most of the salts are observed in the region of hydrides were found to give high yields. In contrast, the use of lithium, sodium, and potassium O metals is impractical, because of their low reactivity LiH II RCSLi (1) and of covering of these metals by the product [3]. 1 Rubidium- (4) and caesium thiocarboxylates (5) have been obtained, however, by using rubidium O NaH II and caesium acetates as the metal sources [4]. The RCSNa (2) reaction conditions, yields, and spectral data are 2 collected in Tables I-V. O O The alkali metal thiocarboxylates (1-5), except II KH II caesium thioacetate (5 a), are thermally stable in RCSH ->• RCSK (3) 3 the solid state and did not change within 6 months or more at room temperature. In general, the li- O thium (1) and sodium salts (2) are strong hygro- CH3C02Rb II >• RCSRb (4) scopic, as compared with the corresponding potas- 4 sium (3), rubidium (4) and caesium salts (5). Espe- O

CH3C02Cs II • RCSCs (5) * Reprint requests to Dr. S. Kato. 5 0340-5087/83/1200-1585/$ 01.00/0 Scheme 1.

Dieses Werk wurde im Jahr 2013 vom Verlag Zeitschrift für Naturforschung This work has been digitalized and published in 2013 by Verlag Zeitschrift in Zusammenarbeit mit der Max-Planck-Gesellschaft zur Förderung der für Naturforschung in cooperation with the Max Planck Society for the Wissenschaften e.V. digitalisiert und unter folgender Lizenz veröffentlicht: Advancement of Science under a Creative Commons Attribution Creative Commons Namensnennung 4.0 Lizenz. 4.0 International License. 1586 S. Kato et al. • A Convenient Preparation of Anhydrous Alkali Metal Thiocarboxylates

1450-1540 cm-1, as characteristic intense bands. Experimental Ring substitution by methyl, methoxy or nitro Melting points were determined using a Yanagi- group or chlorine atom in the ortho-, meta-, and moto micro melting point apparatus and are un- , , , f ,u corrected. The IR spectra were measured on a para-position does not cause large shifts of the JASC0 grating IR s£ectrophotometer IR.G. The carbonyl stretching vibration. UV and Visible spectra were obtained with a

Table I. Physical properties of lithium thiocarboxylates (1).

No. RC(0)SLi Time Solvent Method3, Yield13 M.p.c IR [cm-1]d UV [nm]e [%] R [h] n-C6Hi4/Et20 [°C] fasC = 0 Amax (log e)

la CöHS 24 5:1 A 100 206 1509 282 (3.65) 286 sh (3.64)

lb 4-CH3C6H4 42 5:1 B 49 157 1500 241 (3.93) 284 (3.74) 286 sh (3.73)

lc 4-ClC6H4 18 5:1 B 67 191 1481 239 (3.81) 1496 290 sh (3.50) 299 (3.53) ld 4-CH3OC6H4 20 2:1 A 33 132 1502 256 (3.88) 293 (3.81) le 4-N02C6H4 20 1:1 A 80 93 1512 262 (3.92) 354 (3.50)

a A = the use of excess thio acid, B = the use of excess of LiH; b isolated yield; c decomposition; d KBr; e EtOH.

Table II. Physical properties of sodium thiocarboxylates (2).

No. RC(0)SNa Time Solvent Yield3 M.p.b IR [cm-1]0 UV [nm]d [%] R [h] n-C6Hi4/Et20 [°C] VasC=0 A max (log e)

2a CH3 20 1:10 90 173 1517 249 (3.47) 1551 1562 2b CÖHÖ 18 10:1 66 217 1521 282 (3.65) 295 (3.63) 2c 2-CH3C6H4 20 2:1 92 64(?) 1524 258 (3.69) 2d 3-CH3CeH4 18 2:1 100 197 1505 284 (3.71) 294 sh (3.65) 2e 4-CH3C6H4 18 10:0 87 206 1502 285 (3.81) 299 (3.80) 2f 2-ClC6H4 20 2:1 84 67 ( ?) 1527 255 sh (3.72) 2g 3-CLCGH4 20 2:1 85 214 1502 288 (3.56) 295 sh (3.53) 2h 4-ClC6H4 20 1:1 86 259 1504 288 (3.72) 297 (3.76) 2i 4-CH3OC6H4 18 2:1 55 213-218 1506 258 (3.97) 1519 294 (3.90)

4-N02C6H4 18 1:1 98 222 1491 260 (4.04) 2j 1521

a The isolated yield; b decomposition; c Nujol; d EtOH. 1587 S. Kato et al. • A Convenient Preparation of Anhydrous Alkali Metal Thiocarboxylates

Table III. Physical properties of potassium thiocarboxylates (8).

No. RC(0)SK Time Solvent Yielda M.p.b IR [cm-1]0 UV [nm]d [%] R [h] n-C6Hi4/Et20 [°C] VasC = 0 Amax (log e)

3a CH3 76 0:10 79 131 1528 249 (3.90) 3b C6H5 20 4:1 81 202 1523 283 (3.75) 295 (3.74) 3c 2-CH3C6H4 44 1:1 84 40 1502 260 (3.66) 1532 3d 3-CH3C6H4 18 4:1 97 184 1532 291 (3.63) 296 sh (3.57)

3e 4.CH3C6H4 18 5:1 92 210 1516 283 (3.84) 293 (3.84)

3f 2-ClC6H4 68 1:2 85 148 1512 232 sh (4.02) 255 (3.92) 3g 3-CIC6H4 43 0:10 99 248 1526 288 (3.83) 299 sh (3.79)

3h 4C1C6H4 18 2:3 96 210 1523 290 sh (3.78) 298 (3.80)

3i 4-CH3OC6H4 68 1:3 74 176 1509 257 (4.09) 291 (4.02)

3j 4-N02C6H4 68 0:10 48 196 1520 259 (4.11) 340 (3.74)

a The isolated yield; b decomposition; c Nujol; d EtOH.

Table IV. Physical properties of rubidium thiocarboxylates (4).

No. RC(0)SRb Time Solvent Yielda M.p.b IR [cm-1]0 UV [nm]«1 [%] R [h] n-C6Hi4/Et20 [°C] faSC = 0 Amax (log e)

4a CH3 50 0:10 94 206 1525 250 (3.69) 4b CßHÖ 17 2:1 99 143 1520 282 (3.63) 296 (3.62) 4c 2-CH3C6H4 44 1:4 79 94 1532 256 (3.81) 1543

4d 4-CH3C6H4 44 1:1 99 185 1527 286 (3.78) 294 sh (3.74) 4e 4-CH3C6H4 14 4:1 99 198 1524 283 (3.85) 294 (3.84) 4f 2-ClC6H4 44 1:4 81 127 1510 247 sh (4.17) 4g 3-CIC6H4 68 0:10 77 208 1529 288 (4.14) 297 sh (4.11) 4h 4-ClC6H4 44 1:2 98 232 1523 291 sh (3.73) 300 (3.76)

4-CH3OC6H4 60 1:2 94 118 1512 293 (3.92) 4i * 4j 4-N02C6H4 68 0:10 95 196 1520 259 (4.11) 340 (3.74)

a The isolated yield; b decomposition; c Nujol; d EtOH. 1588 S. Kato et al. • A Convenient Preparation of Anhydrous Alkali Metal Thiocarboxylates

Hitachi 124 spectrophotometer. Elemental analyses hydride (20 — 25% in oil) was purchased from Alfa were performed by the Elemental Analysis Center products. Rubidium and caesium acetates were of Osaka University, and Alfred Bernhardt Ana- commercial grade and dried under reduced pressure lytical Laboratory, Engelskirchen (Germany). at 140 ~ 150 °C. 4-Bromophenacyl bromide and thioacetic acid are commercial grade and used without Materials further purification. Other thiocarboxylic acids were Lithium and sodium hydrides were reagent grade prepared by acidolysis of the corresponding piperi- and the former was triturated before use. Potassium dinium [5] or potassium thiocarboxylates [2 b] with

Table V. Physical properties of caesium thiocarboxylates (5).

No. RC(0)SCs Reaction Solvent Yielda M.p.b IR [cm-1]0 uv k [%] R Time [h] n-C6HI4/Et20 [°C] VasC = 0 A max (log e)

5a CH3 73 0:10 94 147 1520 249 (4.02) 5b C6H5 18 5:1 95 159 1526 282 (3.76) 293 (3.75) 5c 2-CH3C6H4 44 2:5 98 111 1492 259 (3.74) 5d 3-CH3C6H4 68 1:1 94 181 1528 285 (3.81) 294 sh (3.75) 5e 4-CH3C6H4 18 4:1 96 194 1523 242 (4.06) 283 (3.93) 291 sh (3.91)

5f 2-ClC6H4 66 1:3 97 134 1481 242 (3.73) 1502 252 sh (3.72)

5g 3-ClC6H4 44 0:10 88 173 1529 289 (3.95) 296 sh (3.93)

5h 4-ClC6H4 24 2:3 95 187 1520 241 (4.02) 289 sh (3.72) 299 (3.75)

5i 4-CH3OC6H4 68 1:2 91 168 1514 257 (4.07) 292 (3.99)

5j 4-N02C6H4 68 0:10 70 158 1513 259 (4.00) 1573 338 (3.65)

a The isolated yield; b decomposition; c Nujol; d EtOH.

Table VI. Elemental analyses.

No. RC(0)SM Formula Elemental analyses [% ] R M (Mol. weight) C H S

2e 4-CH3C6H4 Na C8H7OSNa Calcd 55.15 4.06 (174.2) Found 55.51 4.36

3e 4-CH3C6H4 K C8H7OSK Calcd 50.49 3.72 (190.3) Found 50.71 3.95

4b CÖHÖ Rb C7H5OSRb Calcd 37.75 2.27 14.40 (222.7) Found 37.57 2.37 14.38

4e 4-CH3C6H4 Rb C8H7OSRb Calcd 40.59 2.99 13.54 (236.7) Found 39.88 3.03 13.64 5b CEHÖ Cs C7H5OSCS Calcd 31.13 1.87 11.87 (270.1) Found 30.82 1.97 11.90

5e 4-CH3C6H4 Cs C8H7OSCS Calcd 33.82 2.49 11.28 (284.1) Found 33.78 2.66 11.07 1589 S. Kato et al. • A Convenient Preparation of Anhydrous Alkali Metal Thiocarboxylates conc-HCl and distilled (for 3-methylthiobenzoic acid) Lithium 4-chlorothiobenzoate (ld) (Method B) or dried over anhydrous sodium or magnesium A solution of 4-chlorothiobenzoic acid (0.516 g, sulfate before use. The solvents were carefully dried 3 mmol) in a mixed solvent (20 ml) of w-hexane/ether by the use of sodium metal and distilled before use. (5:1) was added to a suspension of lithium hydride Typical procedures for the lithium (1), sodium (2), (6 mmol) in the same solvent (10 ml) at —78 °C and potassium (3), rubidium (4) and caesium thio- the reaction mixture was stirred at this temperature carboxylates (5) are described below. All manipula- for 3 h and then at room temperature for 15 h. The tions were carried out under argon or nitrogen excess of lithium hydride was filtered out, followed atmosphere. The reaction conditions, yields, physical by washing with ether (5 ml x 2). To the combined properties, and elemental analyses were summarized filtrate and the washings n-hexane (20 ml) was in Tables I-VI. added and the solution was then concentrated to ca. 20 ml. Filtration of the resulting precipitate, fol- Lithium thiobenzoate (la) (Method A) lowed by washing with %-hexane (5 ml X 2) yielded lithium 4-chlorothiobenzoate (1 c) as slightly yellow A solution of freshly prepared thiobenzoic acid microfine crystals. (2 mmol) in w-hexane/ether (5:1) (30 ml) was added dropwise to a suspension of lithium hydride (1 mmol) in w-hexane (3 ml) at —78 °C and the reaction Sodium thioacetate (2 a) mixture was stirred at this temperature for 3 h and A solution of thioacetic acid 0.152 g (2 mmol) in then at room temperature for 20 h. Filtration of the ether (30 ml) was added dropwise to a suspension of precipitate, followed by washing with w-hexane sodium hydride (1 mmol) in n-hexane (20 ml) at (10ml) gave lithium thiobenzoate (la) .as slight —78 °C and the reaction mixture was stirred at yellow needles. room temperature for 16 h. Filtration of the precipi-

Table VII. Physical properties of a-(acylthio)-4-bromoacetophenone (6).

No. R Yielda M.p. IR [cm-i]* iH NMR0 [%] [°C1 J>C = 0 Ö

6a CH3 89 (Li) 68-69 1687 2.44 (s, 3H, CHs), 4.40 (s, 2H, CH2), 87 (Na) 7.6-8.0 (m, 4H, Ar) 93 (K) 93 (Rb) 89 (Cs) 6b CßHÖ 89 (Na) 130-131 1656 4.52 (s, 2H, CH2), 7.4-8.1 (m, 9H, Ar) 1686

6c 2-CH3C6H4 95 (Li) 105-107 1663 2.39 (s, 3H, CH3), 4.48 (s, 2H, CH2), 95 (Na) 1679 7.2-8.0 (m, 8H, Ar) 92 (K) 85 (Rb) 98 (Cs)

6d 3-CH3CEH4 94 (Na) 104-105 1645 2.40 (s, 3H, CH3), 4.51 (s, 2H, CH2) 1679 7.3-8.0 (m, 8H, Ar)

6e 4-CH3C6H4 91 (K) 138-139 1648 2.49 (s, 3H, CH3), 4.48 (s, 2H, CH2), 1682 7.1-8.0 (m, 8H, Ar)

6f 2-ClC6H4 85 (K) 102-103 1675 4.54 (s, 2H, CH2), 7.2-8.0 (m, 8H, Ar) 6g 3-ClC6H4 89 (Rb) 119-121 1650 4.52 (s, 2H, CH2), 7.2-8.0 (m, 8H, Ar) 1679

6I1 4-ClC6H4 97 (Cs) 140-142 1653 4.52 (s, 2H, CH2), 7.3-8.0 (m, 8H, Ar) 1681

6i 4-CH3OC6H4 73 (Cs) 123-125 1645 3.86 (s, 3H, CH30), 4.50 (s, 2H, CH2), 1681 6.8-8.1 (m, 8H, Ar)

4-N02C6H4 42 (Cs) 173-175 1660 4.58 (s, 2H, CH2), 7.6-8.4 (m, 8H, Ar) 6j 1676

a The isolated yield; the braket is the starting thioates; b KBr; c CDCI3. 1590 S. Kato et al. • A Convenient Preparation of Anhydrous Alkali Metal Thiocarboxylates täte, followed by washing with w-hexane (5 ml x 3), dropwise to a suspension of rubidium acetate yielded sodium thioacetate (2 a) as colorless micro- (1 mmol) in the same mixed solvent (10 ml) at 0 °C fine crystals. and the reaction mixture was stirred at room temperature. Filtration of the precipitate, followed by Aromatic sodium thiocarboxylates (2b-j) washing with %-hexane (5 ml x 3) and then ether (5 ml x 3) yielded rubidium thiocarboxylates (4) as A solution of freshly prepared thiocarboxylic acid colorless or slightly yellow microfine crystals. (ca. 2 mmol) in w-hexane/ether (1:1) (30 ml) was Rubidium 2-methyl-(4 c), 2-chloro-(4f) and 3- added dropwise to a suspension of sodium hydride chlorothiobenzoates (4g) were purified by Soxhlet (1 mmol) in %-hexane (3 ml) at 0 °C and the reaction extraction with ether for 48 h. mixture was stirred for 18 h. Filtration of the resulting precipitate, followed by washing with n-hexane (5ml x 3) and then ether (5ml x 3) yielded Caesium thiocarboxylates (5) sodium thiocarboxylates (2b-j) as colorless or slightly yellow microfine crystals. A solution of freshly prepared thiocarboxylic acid (ca. 2 mmol) in n-hexane/ether (30 ml) was added Potassium thioacetate (3 a) dropwise to a suspension of caesium acetate (1 mmol) in the same solvent (5 ml) at 0 °C and the reaction A solution of thioacetic acid 0.228 g (3 mmol) in mixture was stirred at room temperature. Filtration ether (45 ml) was added dropwise to a suspension of of the precipitate, followed by washing with n- potassium hydride (1.8 mmol) in ether (4 ml) at hexane (5 ml x 3) and then ether (5 ml x 2) yielded — 78 °C for 45 min and the reaction mixture was caesium thiocarboxylates (5) as colorless or slightly stirred at room temperature for 65 h. Filtration of yellowT microfine crystals. the precipitate, followed by washing with ether Caesium 4-nitrothiobenzoate (5j) was purified by (5 mix 7), yielded 0.162 g' (79%) of potassium Soxhlet extraction with ether for 48 h. acetate (3 a) as white microfine crystal. A typical procedure is described for conversion of alkali metal thiocarboxylates (1-5) to a-(acylthio)- Aromatic potassium thiocarboxylates (3b-j) 4-bromoacetophenones (6). Their physical properties were summarized in Table VII. A solution of freshly prepared thiocarboxylic acid (ca. 2 mmol) in %-hexane/ether (25 ml) was added dropwise to a suspension of potassium hydride a-(Acetylthio)-4-bromoacetophenone (6a) (1 mmol) in %-hexane (3 ml) at —20 °C and the reaction mixture was stirred for 20 h. Filtration of Sodium thioacetate (0.196 g, 2 mmol) and 4- the precipitate, followed by washing with n-hexane bromophenacyl bromide (0.56 g, 2 mmol) were stir- (5 ml x 2) and then ether (5 ml x 2), yielded potas- red in anhydrous methanol (60 ml) at room tem- sium thiocarboxylates (3b-j) as colorless or slightly perature for 2 h. After the solvent was evaporated yellow microfine crystals. under reduced pressure, the residue was dissolved in ether (200 ml) followed by washing with water (100 ml x 4) and drying on anhydrous magnesium Rubidium thiocarboxylates (4) sulfate. Evaporation of the ether and subsequent A solution of freshly prepared thiocarboxylic acid recrystallization from n-hexane yielded 0.585 g (ca. 2 mmol) in w-hexane/ether (25 ml) was added (87%) of 6 a as colorless needles.

[1] C6H5C(0)SNa: a) V. V.Savent, J.Gopalakrishnan, [2] a) S. Kato, K. Itoh, R. Hattori, M. Mizuta, and and C. C. Patel, Inorg. Chem. 9, 749 (1970). T. Katada, Z. Naturforsch. 33b, 976 (1978); C6H5C(0)SK: b) S. Kato, S. Yamada, H. Goto, K. Terashima, b) P. Novel and D. S. Tarbell, Org. Syn., Coll. M. Mizuta, and T. Katada, Z. Naturforsch. 35b, Vol. 4, p. 924 (1963); 458 (1980). c) O. Kvm, Ber. 32, 3532 (1899); [3] The salts formed cover the surface of these metals. d) E. Fromn and P. Schmoldt, Ber. 40, 2861 In addition, potassium metal sticks to the flask (1907); during the reaction. e) E. E. Reid, J. Am. Chem. Soc. 43, 439 (1910); f) R. S. Shelton and T. H. Rider, J. Am. Chem. [4] The preparation of rubidium and caesium Soc. 58, 1282 (1930). hydrides is very difficult. RC(0)SLi, Rb, and Cs: No preparation has been [5] S. Kato, W. Akada, and M. Mizuta, Int. J. Sulfur described in the literature. Chem. A 2, 279 (1972).