Sulfur analogue

Thiomahc acid [70-49-5] (mercaptosuccinic acid), C H O S, mol wt = 150.2, is a sulfur analogue of malic acid. The properties of the crystalline, soHd thiomalic acids ate given in Table 6. The racemic acid has the following acid dissociation constants at 25°C pTf i — 3.30 pffc2 — 4.94. 

In the period following World War I and during World War II, a wide variety of sulfur analogues of mustard were investigated and many potent vesicants were discovered. Each had two 2-chloroethyi groups attached to a sulfur atom. Examples of such compounds are... 

Many compounds capable of chelation have been tested for antimicrobial properties. Those showing positive results include saHcylaldoxime [94-67-7] l-nitroso-2-naphthol [131-91-9] mercaptobenzothiazol [149-30-4], dimethylglyoxime [95-45-4], saHcylaldehyde [90-02-8], cupferron [135-20-6], phenanthroline [66-71-7], isoniazid [54-85-3], thiosemicarbazones, the sulfur analogue of oxine, and numerous antibiotics (qv) including tetracyclines. Whether these compounds function exclusively, partially, or at all by virtue of their abiHty to chelate is open to debate. 

Amino and sulfur analogues of pyrazolones also yield the aromatic quaternary salt (231 X = NH or S). If the pyrazole bears a substituent with a second pyridine-like nitrogen atom, an intramolecular bridge can be formed by reaction with a dihalogenoalkane. Thus pyrazol-I -ylpyridines react with 1,2-dibromoethane to form (233) (81JHC9). 

Other routes to oxocarbenes are the a-elimination of bromine from a,a-dibromo ketones (73JA2708, 73JA5416), and the elimination of CO2 or COS from dioxolenones (vinylene carbonates) or their sulfur analogues. The former reaction has not been investigated with regard to oxirene involvement the latter is discussed in Section 5.05.6.3.5. The formation of an oxocarbene from a chlorooxirane was mentioned in Section 5.05.6.3.2. 

Any heterocycle containing the OCH=CH moiety can in principle extrude the superfluous fragment and form oxirene, as illustrated for a five-membered ring in Scheme 105. Probably the most propitious AB fragment would be nitrogen, but the required 1,2,3-oxadiazole (123) is unknown (see Chapter 4.21), probably because of ready valence tautomerization to diazoethanal (Scheme 106) (this approach has been spectacularly successful with the sulfur analogue of (2) (8UA486)). The use of (123) as an oxirene precursor is thus closely linked to the important diazo ketone decompositions discussed in Section 5.05.6.3.4(f). 

There are notable differences in both structures and stabilities for binary N-O and S-N anions (Section 5.4). The most common oxo-anions of nitrogen are the nitrite [N02] and the nitrate anion [NOs] the latter has a branched chain structure 1.1. The sulfur analogue of nitrite is... 

Sulfur analogues of well known organic compounds with NO (nitroso) or NO2 (nitro) functionalities also exhibit different stabilities and/or structures compared to those of RNO or RNO2. For example, there are no stable C-thionitroso compounds RN=S (R = alkyl, aryl), although Ai,/V -dimethylthionitrosoamine Mc2NNS can be isolated (Section 10.2). 

Unlike the stable molecule N2O, the sulfur analogue N2S decomposes above 160 K. In the vapour phase N2S has been detected by high-resolution mass spectrometry. The IR spectrum is dominated by a very strong band at 2040 cm [v(NN)]. The first ionization potential has been determined by photoelectron spectroscopy to be 10.6 eV. " These data indicate that N2S resembles diazomethane, CH2N2, rather than N2O. It decomposes to give N2 and diatomic sulfur, S2, and, hence, elemental sulfur, rather than monoatomic sulfur. Ab initio molecular orbital calculations of bond lengths and bond energies for linear N2S indicate that the resonance structure N =N -S is dominant. 

In spite of the hazardous nature of Sc4N4, this binary selenium nitride has been used for the synthesis of other Se-N compounds, all of which have sulfur analogues (Scheme 5.2). " However, safer alternatives to the use of Sc4N4, e.g., selenium-nitrogen halides and silicon-nitrogen-selenium reagents, are available for the development of Se-N chemistry. ... 

The MS2N2 complexes and their selenium analogues are readily protonated at the nitrogen attached to the metal (Eq. 7.5). Competitive studies show that the selenium complex is a stronger base than its sulfur analogue. 

Diazenes of the type REN=C(R )N=NC(R )=NER have a rich structural chemistry. The selenium derivatives 15.11a,b display a cis,trans,cis conformation with two short l,5-Se N contacts (2.65 A). Several sulfur analogues, e.g., 15.1c, have the same structure, but a different cis,trans,cis conformer 15.12 with two 1,4-S N contacts (2.83 A) has also been characterized. A third type of diazene is the trans,trans,trans isomer 15.13a,b with no intramolecular short contacts. ... 

Isothiazole is the sulfur analogue of isoxazole. No member of the group is known. A necessary condition for the development of this field is the preparation of the unknown thiohydroxylamine. This reasonable assessment of the position in 1947 was not in fact true. 

Preparation of the sulfur analogue involves as the first step cyclization of the terephthalic acid derivative 92. The acid is then converted to the acid chloride and this is allowed to react with diazomethane. Rearrangement of the resulting diazoketone (95) under the conditions of the Arndt-Eistert reaction leads to the homologated acid. 

The sulfur analogue of the Hauser ortho-substitution rearrangement provides access to an arylacet-ic NSAID. Reaction of the aminobenzophenone 176 with ethyl methylthioacetate and tert-butyl hypochlorite gives the intermediate 178. The reaction probably proceeds by way of formation of the S-chlorinated sulfonium derivative 177 displacement on sulfur will lead to the salt 178. Treatment with triethylamine leads initially to the betaine 179. Electrocyelic rearrangement of that transient intermediate leads, after rearomatization, to the homoanthranilic acid 180. Internal ester-amine interchange leads then to indolone 181 [45]. The thiomethyl group is then removed with Raney niekel. Saponifieation of intermediate 182 affords bromfenac (183) [46J. 

Benz Derivatives of Pyrans, Pyrones, and Their Sulfur Analogues. 298... 

Benzo[h]selenophene is more reactive than the oxygen and sulfur analogues, but less so than benzo[b]tellurophene, although substituents may modify this to some extent [90AHC(47)181]. 

Dimethyl-2,l,3-benzoselenadiazole was brominated on the methyl groups by NBS (87CB1593), but halogenation of the unsubstituted compound occurred, as with the sulfur analogue, at the 4(7)-position initially. Polybromination can occur (64JGU3063). 

Much more is known about the sulfur analogues, especially the benz derivatives of 1,4-thiazine. Bromination of AH-1,4-benzothiazine 1,1-dioxide occurred in the 2-position (68TL1041). 

The synthesis of a new sulfur analogue of angelicin, a thiopyrano[2,3-e]benzofuran, was reported <96JOC4842>. The reaction of 3(2//)-benzofuranone with SjClj yields bis-2-spirocoumaranoylidenetetrathiane instead of oxindigo (an oxidative coupling of a coumaranone) (Scheme 12, <96T1961>). 

The thiol 48 (with R R, R = H) undergoes intramolecular cychsation in THF, in the presence of AIBN under UV irradiation, to give a 2-phosphonothiolane [36], a phosphorus and sulfur analogue of proline. More recently, an asymmetric version of the sequence, [2,3]-sigmatropic rearrangement and radical cychsation, has been carried out (see Sect. 5.1.1.) [41]. 

The chalcogen-capped clusters M M2Co(/(3-S)(CO)s()/ -CsH5) (M M2 = MoEc, MoRu, WFe) and MoFeCo(/r ,-Se)(CO)H()) -CsH3) underw ent a one-electron, quasi-reversible reduction. Addition of an electron proceeded more readily for the clusters w ith the lighter metals and for the selenium capped cluster relative to its sulfur analogue. 

Trigonal selenium is variously called metallic gray or black selenium and occurs in lustrous hexagonal crystals, which melt at 220.5 °C. Its structure, which has no sulfur analogue, consists of infinite, unbranched helical chains. Its density, 4.82 g cm , is the highest of any form of the element. Trigonal selenium is a semiconductor (intrinsic p-type with a rather indirect transition at about 1.85 eV [5]), and its electronic and photoelectric properties are the basis for many industrial uses of this element. 

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