Hydrosulfide ion

Trihalomethyl groups have a-constants similar to those of the halogens but seem to be generally much less reactive than chlorine. However, convenient displacement of the former is often possible. Chlorine is more reactive than the trifluoromethyl group in 4-chloro-and 4,6-dichloro-2-trifluoromethylpyrimidine and the 5-nitro derivative of the latter thus ammonia or hydrosulfide ion gave the 4-and 4,6-analogs. In the isomeric 2,6-dichloro-5-nitro-4-trifluoro-... 

Disubstitution of 2,4-dichloropyrimidine with thiourea proceeds more readily than with hydrosulfide ion, principally because the former intermediate (229) contains the activating, cationic acylated thio group compared to the highly anionized mercapto group in the latter reaction. 

Diamino-6,6-dialkyl-7-oxo derivatives were converted with POCI3 (106°, 46 min) to 7-chloro analogs which were then 7-thionated with hydrosulfide ion. °... 

The stability of chalconide (ionic) compounds decreases from oxygen to tellurium treatment with water produces XH- with X = O or S (hydroxyl and thiol radicals, respectively), but XH2 with X = Se or Te. On warming, aqueous solutions of HS evolve hydrogen sulfide, evidencing that the hydrosulfide ion is much less stable than hydroxide. 

DR. WILLIAM TROGLER (Northwestern University) I have a question about the status of sulfur nucleophiles. The calculations suggested that hydrosulfide ion was a very poor nucleophile. It has always puzzled me, at least in organic chemistry, that sulfur is such a great nucleophile. Have you done any experiments ... 

H. P. Stephens and J. W. Cobble [Inorg. Chem. 10, 619-625 (1971)] give the following expression for the pATa of the aqueous hydrosulfide ion HS- over the temperature range 0-100 °C at infinite dilution ... 

A preliminary electrochemical investigation of l,2-dimethyl-3-thio-formylindolizine in acetonitrile using mercury electrodes indicated that an initial quasi-reversible electrochemical reduction was followed by an irreversible process with possible loss of hydrosulfide ion.170... 

The presence of a 4-(4-dimethylaminophenyl) group enhances the visible absorption differences between the pyrylium and thiopyrylium salt analogues. Thus, on reaction of 625 with hydrosulfide ion a change in hue from magenta (540 nm) to blue (580 nm) is observed this color change serves as the basis for a new chemodosimeter selective for hydrosulfide (Scheme 240) <2003JA9000>. 

Note This process can be done directly with hydrosulfide ion or indirectly (via an unisolated thiouronium intermediate) using thicurea. 

Since ACi — 10 and K2 10-7, the equilibrium in equation 7-10 strongly favors the presence of hydrosulfide ions and for all practical purposes, sulfide ions can be considered to be absent (Fig. 7-20). The concentration of... 

The overall rate of the bulk delignification in kraft pulping, during which the variations in hydroxyl and hydrosulfide ion concentrations are moderate, follows pseudo-first-order kinetics, approximately in conformity with the following equation ... 

A normal heating period contributes to the H factor by 150-200, and 1500-2000 are needed for a complete kraft cook. Within the bulk delignifi-cation phase the relative reaction rate is doubled when the temperature is increased by about 8°C. If the hydroxide and hydrosulfide ion concentrations vary in a reproducible manner the H factor will predict the degree of delignification with sufficient precision. 

Free Phenolic Structures Containing /3-Ary I Ether Bonds The first step of the reaction involves the formation of a quinone methide from the phenolate anion by the elimination of a hydroxide, alkoxide, or phenoxide ion from the a-carbon (Fig. 7-25). The subsequent course of reactions depends on whether hydrosulfide ions are present or not. In the latter case (soda pulping), the dominant reaction is the elimination of the hydroxymethyl group from the quinone methide with formation of formaldehyde and a styryl aryl ether structure without cleavage of the /8-ether bond (Fig. 7-26). When hydrosulfide ions are present (strong nucleophiles) they react with the... 

Fig. 7-25. Main reactions of the phenolic /8-aryl ether structures during alkali (soda) and kraft pulping (Gierer, 1970). R = H, alkyl, or aryl group. The first step involves formation of a quinone methide intermediate (2). In alkali pulping intermediate (2) undergoes proton or formaldehyde elimination and is converted to styryl aryl ether structure (3a). During kraft pulping intermediate (2) is instead attacked by the nucleophilic hydrosulfide ions with formation of a thiirane structure (4) and simultaneous cleavage of the /3-aryl ether bond. Intermediate (5) reacts further either via a 1,4-dithiane dimer or directly to compounds of styrene type (6) and to complicated polymeric products (P). During these reactions most of the organically bound sulfur is eliminated as elemental sulfur.

Methoxyl Groups Lignin is partially demethylated by the action of hydrosulfide ions forming methyl mercaptan which is convertible to dimethyl sulfide by reaction with another methoxyl group. In the presence of oxygen, methyl mercaptan can be oxidized further to dimethyl disulfide (Fig. 7-28). Because the hydroxide ions are less strong nucleophiles than hydrosulfide ions, only small amounts of methanol are formed. Methyl mercaptan and... 

Chloro-4,6-diphenyl- and 2-chloro-4,6-dimethyl- -triazines (318) undergo facile nucleophilic displacements with ammonia, amines, and hydrazine, with alkoxide, or with hydrosulfide ions, A convenient synthesis of monoamino-s-triazines in high yield is the reaction of 2-phenoxy-s-triazine (319) with ammonia or aliphatic amines (30-70°) or with aniline (120°). Triphenoxy- -triazine (320) reacts with all classes of amines without side-reactions... 

Treatment of 1,3-dihalopropanes with sulfide or hydrosulfide ion has been used extensively to prepare thietanes. Yields reported vary from... 

Dimethyl- and 3,3-diethyl-l,3-thiasilacyclobutanes are obtained by intramolecular cyclization of the bis(chloromethyl)silane with hydrosulfide ion, as exemplified by the synthesis of 522 or by an intramolecular hydro-silation, as exemplified by the synthesis of 523. A chloroplatinic acid catalyst (Speiers catalyst) also has been used for the hydrosilation... 

Methylfluorosulfonate and 1 -methyl-2-oxo-l, 2-dihydropyrazine gave a quantitative yield of 1,4-dimethyl-2-oxo-l, 2-dihydropyrazinium fluorosulfonate, which reacted instantaneously and exothermically at room temperature and in high yields with hydroxide ion, hydrosulfide ion, and ammonia to give interesting new cage systems (1130). 

The answers to these questions aren t straightforward. Part of the problem is that the term nucleophilicity is imprecise. The term is usually taken to be a measure of the affinity of a nucleophile for a carbon atom in the Sj,-2 reaction, but the reactivity of a given nucleophile can change from one reaction to the next. The exact nucleophilicity of a species in a given reaction depends on the substrate, the solvent, and even the reactant concentrations. It s therefore best to define a set of standard conditions and study the relative reactivity of various nucleophiles on a single substrate in a single solvent system. Much work has been carried out on the Sm2 reactions of bromomethane in aqueous ethanol, with the following results. Note that hydrosulfide ion (HS ) is approximately 125,000 times as reactive as w ater. 

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