Thio carbonates

As indicated above, the traditional base-catalysed hydrolysis of 0,5-dialkyl thio-carbonates for the synthesis of thiols is generally unsatisfactory, as oxidation leads to the formation of disulphides. Under phase-transfer conditions, the procedure produces thioethers to the virtual exclusion of the thiols, as a result of the slow release of the thiolate anions in the presence of the electrophilic ester. However, a simple modification of the reaction conditions provides an efficient one-pot reaction [50] from haloalkanes (Table 4.15) via the intermediate formation of the thermally labile (9-/ert-butyl-5-alkyl dithiocarbonates (Scheme 4.8). 

Dissolve 20 g. of cuprous chloride, CuCl, in the least possible volume of concentrated hydrochloric acid. Cool the solution in ice and slowly add 500 cc. of concentrated ammonia. Keeping the temperature at 0°, add 55 g. of carbon disulfide and shake vigorously at frequent intervals. After standing some 6 days in an ice box at approximately 0°, shining green crystals of the thio-carbonate separate from the solution. Filter off these crystals, wash them with cold water, and quickly dry them on paper. The potassium salt can be made with slight modifications of these directions. 

Fig. 1.44. Cyclization-free defunctionalization of the thio-carbonic add derivative from Figure 1.42.

We explored other thiocarbonyl derivatives including xan-thates (e.g. 19), thionoimidazolides (e.g. 20) and thio-carbonates. The last convert a glycol such as 21a via the thiocarbonate 22 and subsequent tin hydride reduction to mainly the primary alcohol 21b. The intermediate opens in such a way as to afford the more stable radical. This reaction is readily applied to nucleosides.910... 

Extension of equation (43) to include sulphur or nitrogen led to complications. The elimination of CO2 from S-phenyl methyl thio-carbonate (44) fits the general scheme, but loss of COS from S-methyl... 

By analogy to Eq. 9 the new phosphaalkyne may also be obtained from 0,0-diethyl thio-carbonate and lithium bis(trimethylsilyl)phosphanide dissolved in 1,2-dimethoxyethane. Both educts react at about 0 °C to give ethoxy trimethylsilane and the finally isolated compound tris(l,2-dimethoxyethane-0,0 )-lithium 2-phosphaethynylsulphide (Eq. 12). Emphasis should be laid on its NMR parameters (5 P -121.3 S C 190.8 ppm Jcp 18.2 Hz [Dg]-THF solution) in that they correspond much more to the values of diisopropylaminophosphaalkyne (8 P -99.6 S C 152.2 ppm Jcp 14.7 Hz [31]) than to those of bis(l,2-dimethoxyethane-0,0 )lithoxymethylidynephosphane (5 P -384.2 166.6 ppm ... 

Xanthx Acid.—Another solvent of cellulose is xanthlc acid, also called xanthonic or xanthogenic acid. Xanthic acid is the ethyl ether of -di-thio-carbonic acid. Its formula is HS-CS-OC2H5. When heated with water to 500° under pressure cellulose is dissolved and undergoes decomposition. 

Viscose Silk.—III. From Cellulose Xanthate. We have referred to the solvent action of xanthic acid, which is the ethyl ether of di-thio-carbonic acid, viz., HS-CS-OC2H5. When sodium cellulose is dissolved in xanthic acid the cellulose is in the form of sodium cellulose xanthate. A solution properly prepared by treating cellulose with sodimn hydroxide and carbon di-sulphide in the presence of benzene or carbon tetra-chloride, in which polymerization of the cellulose compound is effected, is decomposed by forcing capillary streams of the solution into a solution of ammonium sulphate. The cellulose is thus obtained as in the other processes in the form of fine filaments of a hydrated cellulose possessing silk-like properties. Artificial silk of this type is known as viscose silk and is made in large quantities. In 1914 about 20,000,000 pounds of artificial silk were made, of which about 3,000,000 pounds were made in the United States. Most of this product was viscose silk. 

Thiols add to alkenes under photochemical conditions to form thioethers, and the reaction can be done intramolecularly to give cyclic thioethers. Thiols also add to alkynes and with a palladium catalyst, vinyl sulfides can be formed. Thio-carbonates function as thiol surrogates, converting alkenes to alkyl thiol in the presence of TiCl4 and CuO. °... 

The distribution of electron density in the sulfur-containing ligands is modified to allow the thiones to function as two unsymmetrically opposed 4e donors in the complex of type 4. The compound has no metal-metal bond. Behrens and co-workers 30) as well as Seyferth et al. 15) prepared symmetrical complexes in which the ligands are bound similarly to the one drawn below the two iron atoms in 4. In the Behrens compounds, prepared from thioketenes, the a-thio carbon atom is sp hybridized in contrast to the sp hybridization which occurs when the two iron atoms are held together by the O-thioformate groups in Seyferth s compound. The latter group proposed two completely different, competing pathways for the formation of complexes of types 1 and 3. 

In addition, the sulfur atom attaches itself to another a-thio carbon to form a 1,1-dithiolato ligand (see type 3) (31). 

Lithium naphthalenide, THF, 0°C, l-2h, 71-99% yield. Cbz carbonates, thio-carbonates, and carbamates are also cleaved under these conditions. ... 

The term "extrusion reaction" defines reactions in which an atom or group of atoms bonded to two other atoms is lost. Among the most frequently lost atoms or group of atoms are azo, carbonyl, sulfonyl, thio, carbon dioxide. The two atoms formerly bonded to the lost group can become directly bonded together this is the restricted definition of March. ... 

Lactones may in principle be obtained if the olefinic trap is placed on the oxygen side of the xanthate. The more complex sequence in Scheme 11, discovered seren-dipitously, illustrates the construction of such a lactone starting with an aryl thio-carbonate [20]. It also involves the transfer of the aryl group in the penultimate step. 

Barton and his students [24] and, more recently, by other groups [25], The second transformation in Scheme 12 illustrates the conversion of a tartrate-derived thio-carbonate into a malate using hypophosphorous acid [26]. Phosphine-borane complexes have also been proposed as convenient hydrogen atom donors for the deoxygenation [27],... 

For formation of thiols and sulfides on fission of the C-S bond of thio-carbonic acid derivatives see pages 635 and 637. 

Methyl-l -p-tolyl-pyrrolidon-lSI-thio carbons uie-(2)-amid 88, 292. 

With thio carbonic and thio carboxylic acids Fe C2H50C(S)S- 3 solution CHCI3 frozen 81 = 2.193 82 = 2.143 83 = 1.992 9.3 71C8... 

---