Herz salts

While the stoichiometry of the reaction appears simple, the reaction mechanism is not well understood, despite numerous studies,77 and the reaction tipically gives rise to a number of by-products. Purification of Herz salts is best achieved via metathesis to one of a number of more soluble salts (A1C14, BF4 , SbCl6-), which can be recrystallised to a high degree of purity.78... 

A synthesis of benzofused 1,2,3-dithiazolium (Herz) salts by the action of sulfur monochloride on arylamines is the best-known synthesis of this class. Although it has been known for over 80 years (1922DEP360690), it is still in use. This chemistry was reviewed (1957CRV1011) and therefore here we describe the synthesis of heteroannulated 1,2,3-dithiazolium salts and new achievements in their preparation. 

Bis(l,2,3-dithiazoles) represent a new and potentially valuable class of heterocycles. A notable development is the "double Herz condensation" of 2,6-diaminonaphthalenes with sulfur monochloride which afforded naphtho-bis[l,2,3]dithiazole 110 after reduction of di-Herz salt 111 with triphenylantimony... 

Herz salts (89) made from 3-aminopyrazoles (Section 4.11.8.5) give pyrazolo[3,4-r/]-l,2,3-thia-diazoles (90) when subjected to reduction by sodium dithionite followed by nitrozation (Equation (12)) <84JOCl224>. If the reduction is carried out in an inert atmosphere the disulfide (91) is formed which upon nitrozation gives (90) in 63% yield. Notably, benzo-fused Herz salts give benzo-1,2,3-thiadiazoles simply on treatment with nitrozating mixture <84CHEC-I(6)916>. 

Herz salts bearing chlorine at the 6-position 140 react with malononitrile to afford highly colored ylidenes 141 in low to moderate yields (Equation 31) <2002J(P1)315>. The reaction is general but complex few by-products were isolated. 

Structural proof for the Herz salts (5//-pyrazolo[3,4-d]-l,2,3-dithiazol-2-ium chlorides) (29) rests on their UV spectra and chemical reactivity. Two bands were observed in the UV spectra of this series of compounds, one of which was very sensitive to the nature of the substituent at position 6. The similarity between these spectra and those for the known Herz salts of aniline derivatives suggest a similar chromophore <84JOCl224>. The stable sulfur-nitrogen radical (14) has a broadband absorption at 595.5 nm, giving it a blue color <89AG(E)920>. 

The most extensively studied benzo fused ring system within the scope of this chapter is the 1,2,3-benzodithiazolylium cation of general structure (4). Although it was first reported 60 years ago (22GEP360690), and the field (Herz salts) later reviewed (57CRV1011), its controversial mechanism of formation is still not settled. Reaction between primary amines... 

Benzo-fiised 1,2,3-dithiazolyls 38 are prepared by the reduction of readily prepared Herz salts 37 using decamethylferrocene in acetonitrile (Scheme 8) (1999JA969, 2001CJC1352, 2005IC1837). Se and Te derivatives of fused 1,2,3-dithiazolyls can also be prepared in a similar manner and a wide variety of reductants can be used such as octamethylferrocene, hexamethylferrocene, tetramethyl-p-phenylenediamine, and electrochemical reduction (2008IC10100). 

While the Herz reaction provides a convenient route to many dithiazolylium salts, the propensity for chlorination of the aromatic substituent has led to the development of several other approaches to 1,2,3-dithiazolylium salts and... 

Substituted thioindigoid dyes are usually obtained via the appropriate benzenethiol in a Heumann-type synthesis. The final cyclisation of the phenylthioglycolic acid derivative can often be achieved in concentrated sulphuric acid or by using chlorosulphonic acid. Several routes make use of the Herz reaction (Scheme 6.22), in which a substituted aniline is converted into the corresponding o-aminothiophenol by reaction with sulphur monochloride followed by hydrolysis of the intermediate dithiazolium salt [47]. After reaction between the thiol and chloroacetic acid, the amino group is converted into a nitrile group by a Sandmeyer reaction. Hydrolysis of the nitrile leads to the formation of the required thioindoxyl derivative. 

Double Herz condensation of Af-alkylated 2,6-diaminopyridinium salts with sulfur monochloride is an effective procedure for the preparation of bis[l,2,3]dithiazolopyridinium salts 112 (2004CM1564) that were readily reduced to the corresponding dithiazolyl radicals 113 by decamethylferrocene (Scheme 56). 

Synthesis of 1,2,3-dithiazoles is the most extensively studied. The widely used and very long-known Herz reaction of arylamines with S2CI2 to give benzo-l,2,3-dithiazolium salts (Section 4.11.8.5) has been extended to hetarylamines (Scheme 17). More importantly, a new impetus for its investigation and development was provided when benzo-l,2,3-dithiazolyl radicals were shown by Mayer and co-workers to be intermediates. The reaction in a modified form was transformed by the above authors to an effective method for synthesis of this new class of stable radicals. When applied to acyclic enaminoketones the thiosulfinylamine precursor of the free radical could be isolated (Scheme 18). It was also extended to cyclic and acyclic oximes to afford fused and monocyclic... 

Herz s Explosives. Patented in 1923 CA 18, 1573-4 (1924) BritP 207563, several compositions, such as ortho-, and para-nitrated quinone diazides of the polymeric phenols or their metallic salts either (1) as a top charge over a main (base) charge such as Tetryl, TNT, or PETN, or (2) in admixtures with other compounds. Following are the primary and nitrating compounds proposed by von Herz ... 

Azotetrazole was prepd by J. Thiele, and its expl salts were recommended by E. von Herz and by H. Rathsburg for use in detonators. Its derivatives were described by L.F. Aufrieth J.F. Currier in Umv of Illinois Kept, Derivatives of 5-Aminotetrazole , pp 22—23 (1954) (See Vol 1 of Encycl, pp A659 A660)... 

Metallic salts of these compounds were proposed by von Herz to be used in detonators percussion caps. Lead Methylene diisonitramine is specifically mentioned (Refs 1 2)... 

Normal lead styphnate (LS) [Structure (2.10)] was first reported by Von Herze in 1914, although its basic salt, that is, basic LS was prepared by Griess [7] way back in 1874, by the reaction of acidified magnesium styphnate with lead nitrate/acetate in hot aqueous solution. It is precipitated as mono hydrate and consists of reddish-brown rhombic crystals. It is filtered off, washed with water, sieved through a stainless steel sieve and dried. Like other initiatory explosives, it is kept in wet conditions until used. 

A method of preparation of the neutral salt (I) has been given by Herz [45]. He claims that the anhydrous salt crystallizes from an aqueous solution. In the light of other authors works (e.g. Zingaro), it is doubtful whether in such conditions, an anhydrous salt can really be formed. The dehydration of neutral lead styphnate (I) was investigated by Zingaro who found that complete dehydration may be effected by heating the substance at 115°C for 16 hr. At higher temperatures (135-145°C) dehydration takes place more quickly (Fig. 53). Stettbacher [46] reported that in a moist atmosphere anhydrous lead styphnate absorbs water to reform... 

See also Diazochemistry, Diazo hydrocarbons and Diazonium Salts Refs 1) E. von Herz, BritP 207563(1922)... 

C6H(0KXN02)2( N)( 0), yel ndls (from coned aq soln) was prepd by von Herz on treating with.an excess of K nitrite the mononitro-amino-resorcinol, H2N.C H3(OH)2, dissolved in hot coned nitricrsulfuric acid. After prolonged boiling, the soln was cooled and this rendered fine, yel ndls of K salt. The crysts were washed with a small amt of cold water and dried. The salt was patented for use as a primary charge in compd detonators. 

CA 17,1147(1923) (Expl salts of Tetrazole and Triazole or their derivs are used in detonators, percussion caps, etc- These salts may be mixed or pptd simultaneously to form double or mixed crysts with substances such as NH3, nitrophenols, etc or nay also be granulated with paraffin or resins dissolved in C5H6, CC14, etc) 58)E. von Herz,Brit P 187012(1921) USP 1498001(1924) CA 17,1147 (1923) 18,2605(1925)(Mixts of LA LSt for use as expl priming compns are prepd by simultaneous" ly pptg the two salts) 59)H.Rathsburg,BritP 190215(1921) USP 1470104(1923) CA 17,3101... 

H. M. Dawson and J. McCrae, D. P. Konowaloff, and W. Gaus also used soln. of various salts of the alkali metals, and of potassium, sodium, cupric, or barium hydroxide in place of water and also copper sulphate, copper chloride, zinc sulphate, and cadmium iodide while M. 8. Sherrill and D. E. Russ examined the effect of ammonium chromate. W. Herz and A. Kurzer examined the distribution of ammonia between water and a mixture of amyl alcohol and chloroform. Observations on the distribution of ammonia between water and chloroform were made by T. S. Moore and T. F. Winmill, G. A. Abbott and W. C. Bray, and J. M. Bell. J. H. Hildebrand gave for the molar fraction N X104 of ammonia at 1 atm. press., and 25°, dissolved by ethyl alcohol, 2300 methyl alcohol, 2730 and water, 3300. 

Quinone Diazides. E. von Herz (Ref 1) proposed the use of nitrated quinone diazides and tetra-zides of polyhydric phenols or their metallic salts in percussion caps and primers, either as a top charge over a main charge (Tetryl, PETN or TNT), or in mixts with usual primary expls such as LA, MF, etc. Typical compds were 4,6-dinitro-2-quinone diazide, the K salt of dinitro-3-hydroxy quin one diazide, metallic salts of dinitro-4-hydroxyquinone diazide, the Pb salt of dinitro-3,5-dihydroxyquinone diazide, and sym-tetra-nitrodihydroxydiphenylolquinone tetrazide J.E. Burns (Ref 2) proposed the use of nitrated quinone diazides, such as the 2,6-dinitro-2-diazide, with Pb pic rate, Na nitrate, Pb thio-... 

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