Formation of aryliodine(III) derivatives in the nitration of aryl iodides in acetic anhydride

Abstract

Nitration of iodobenzene, o-iodotoluene, and p-iodotoluene in acetic anhydride results in reversible oxidation to aryliodine( 111) compounds prior to the formation of the expected nitro derivatives. p-0x0-[nitrate( phenyl) iodine] [phenyl (trifluoroacetato) iodine] has been isolated from nitration of iodobenzene and its crystal structure determined.When 0-and p-iodo-toluene are nitrated in acetic anhydride the reactions do not go to completion under conditions which bring about complete reaction of the other halogenotoluenes and the iodotoluenes appear to be less reactive than the other halogenotoluenes. This is surprising since nitration of iodobenzene in aqueous sulphuric acid is faster than nitration of the other halogenobenzenes and additivity of substituent effects would suggest that this should also be true of the iodotoluenes. Nitration of p-fluoro-, p-chloro-, and p-bromotoluene in acetic anhydride gives good yields of adducts with nitro ips0 to methyl and lesser amounts of the nitro substitutionThe calculated product distribution for the nitration ofp-iodotoluene is similar to that for p-bromotoluene; however, little adduct is formed from p-iodotoluene.2 Parallel observations have been made on the ortho-halogenotoluenes viz. 1,4-adducts are formed in significant yield from the fluoro, chloro, and bromo derivatives but not from the iodo c~m p o u n d .~We have investigated the nitration of 0-and piodotoluene and of iodobenzene and have resolved these apparent anomalies. Results and DiscussionNitration Reactions.-0-lodotoluene. Nitration was carried out using a mixture of nitric acid, acetic anhydride, and trifluoroacetic anhydride and was followed by 'H n.m.r. spectroscopy. At -20 "C the o-iodotoluene reacted completely over a period of 30 min. The major component of the product mixture had 'H n.m.r. peaks similar to those of o-iodotoluene but shifted approximately 6 0.5 downfield. Some 2-iodo-4-nitroand 2-iodo-5-nitro-toluene were also formed and a minor amount ( c 10% of the product) of diene adduct. When the reaction mixture was worked-up after this time the major component of the isolated product mixture was o-iodotoluene and the major component in the reaction mixture was not present. When the reaction was carried out for an extended period (15 h) at low temperature, or for a shorter period (20 min) at ambient temperature, the first formed product disappeared and the iodonitrotoluenes were obtained. It is evident that the o-iodotoluene was initially converted reversibly into an intermediate from which the o-iodotoluene was regenerated as it was nitrated, or when the mixture was worked up. By analogy with the reaction of iodobenzene (below) this intermediate is assumed to be an o-iodosyltoluene derivative similar to (1). When the nitration was carried out in the absence of trifluoroacetic anhydride the reactions were similar although much slower, even at OOC, and the iodotoluene disappeared over 15 h. Again an intermediate was formed and nitration ensued.p-lodotoluene. Nitration was carried out with n...

Organic Polyvalent Iodine Compounds

“…A distinctive feature of all μ-oxo-bridged iodanes 131 is the bright yellow color due to the + I−O−I + bridging fragment . The available X-ray structural data for 131 (X = ONO 2 , and OCOR , ) is also consistent with the ionic character of the I−X bonds.…”

“…5 However, more recent spectroscopic and X-ray studies revealed the µ-oxo-bridged structure for all stable derivatives of strong inorganic acids. 230,231,285 These compounds are generally prepared by the reaction of PhI(OAc) 2 or PhIO with the respective acids or anhydrides.…”

“…In older reports, some of these compounds, particularly, the nitrate and perchlorate, were incorrectly claimed to have the PhIX 2 structure . However, more recent spectroscopic and X-ray studies revealed the μ-oxo-bridged structure for all stable derivatives of strong inorganic acids. ,, These compounds are generally prepared by the reaction of PhI(OAc) 2 or PhIO with the respective acids or anhydrides.…”

Anhydrides of Real and Hypothetical [Hydroxy(R−O)iodo]benzenes

“…I2 in the λ 5 -iodane 2-iodoxybenzoic acid isopropyl ester ( 32 ; Figure ) has three intermolecular I···O bonds (I2···O2′′, 3.051 Å; I2···O1, 3.191 Å; I2···O5′, 2.560 Å) and one intramolecular bond (I2···O7, 2.698 Å) that likewise produce triangular dodecahedral EDG. Numerous examples of CN 8 with capped pentagonal-bipyramidal EDG appear, including I atoms in tris(acetato−O)iodine(III) ( 33 ; Figure ), [bis(trifluoroacetato−O)iodo]benzene ( 34 ), I1 in μ-oxo[nitrato−O(phenyl)iodine(III)][phenyl(trifluoroacetato−O)iodine(III)] ( 35 ), the (arylsulfonylimino)iodoarenes m -tolylINSO 2 Ph ( 36 ) and m -tolylINSO 2 - p -NO 2 C 6 H 4 ( 37 ), I1 in μ-oxobis[trifluoroacetato−O(phenyl)iodine(III)] ( 27 ), and o -[dichloro(iodo)]nitrobenzene ( 38 ; Figure ) . A third CN 8 geometry is exhibited by the λ 5 -iodane IF 6 − ( 39 ; Figure ): Six primary bonds with F atoms, one intermolecular secondary bond (I···F6′, 2.817 Å), and one unshared pair of electrons are arrayed in a cubic antiprismatic EDG.…”

“…In 1972, Merkushev and co-workers reported the preparation of μ-oxobis[trichloroacetato−O(phenyl)iodine(III)], μ-oxobis[chloroacetato−O(phenyl)iodine(III)], and μ-oxobis[bromoacetato−O(phenyl)iodine(III)] with characterization via elemental analysis and molecular weight determinations. Structures have been determined via X-ray crystallography for μ-oxobis[nitrato−O(phenyl)iodine(III)], μ-oxobis[trifluoroacetato−O(phenyl)iodine(III)], μ-oxobis[trifluoroacetato−O( m -methylphenyl)iodine(III)], μ-oxo[nitrato−O(phenyl)iodine(III)][phenyl(trifluoroacetato−O)iodine(III)], and the diacetato μ-oxodiiodane where the I atoms have a bridging binaphthyl group . Most recently, Nemykin et al have isolated μ-oxobis[acetato−O(phenyl)iodine(III)].…”