Reductivedehalogenationofhalophenolsinsulfite–bisulfatemedium Subbarayappa Adimurthy and Gadde Ramachandraiah * Central Salt and Marine Chemicals Research Institute, G. B. Marg, Bhavnagar 364 002, India Received 5 March 2004; revised 5 May 2004; accepted 6 May 2004 Abstract—TheKHSO 4 –Na 2 SO 3 systemisfoundtobesimpleandinexpensiveforreductiveeliminationofhalogens(Br,I)fromthe corresponding halophenols under reflux conditions in dry methanol. Under similar conditions the reaction is sluggish with chloro- phenols. Ó 2004 Elsevier Ltd. All rights reserved. 1. Introduction In recent years, the halogens on aromatic rings have been used as potential protecting or blocking groups in synthetic organic chemistry. 1;2 Aromatic halides are readily reduced by metal-catalyzed transfer hydrogen- olysis. 3 Theprocessofreductiveeliminationofhalogens from aromatic rings is relatively quite a difficult task. There are reports of the use of Pd(II) salts, to give the corresponding dehalogenated compounds. 4 Generally, debrominations have been carried out in hydrobromic acidinthepresenceofasuitablebrominescavengersuch asanilineorphenolorsodiumsulfite. 2;5 Dehalogenation by direct hydrogenolysis has been accompanied by the reduction of double bonds in the case of unsaturated halides and the formation of amines in case of nitro halides. Dehalogenation of aromatic halides has been reported over palladium deposited on carbon 6 in the presence of a proton donor like limonene and p- menthene at 50–100 °C, but the nitrile group of o/p- chlorobenzonitrile was also reduced. Cortese and Heck 3 have achieved the dehalogenation of aromatic halides without affecting a nitrile group by employing triethyl- ammonium formate/triarylphosphine catalyzed by pal- ladium or palladium acetate at 50–100 °C. Nucleophilic reagents such as LiEt 3 BH 7;8 and 2LiAlH(OCH 3 ) 3 –CuI 9 have been used in dehalogenation reactions. Tyrlik and Wolochowicz 10 have employed a TiCl 3 /3THF–Mg sys- tem for easy reduction and dehydrohalogenation of organic halides under a nitrogen/argon atmosphere obtaining moderately low yields. In earlier communications 11 we have reported dehalo- genation in the presence of H-b zeolite catalyst and dehalonitration of halophenols in HNO 3 . 12 Here, we wish to report our further findings of reductive dehalo- genation of halophenols carried out in a bisulfate (KHSO 4 )–sulfite (Na 2 SO 3 ) medium. The reductive deiodination of 1-iodo-2-naphthol, 1 was chosen as a model reaction and carried out as shown in Eq. 1 over a bed of KHSO 4 (5molequiv)–Na 2 SO 3 (6molequiv) at reflux in dry methanol. The progress of the reaction was monitored by TLC analysis following the production of 2-naphthol, 2. 11 The reaction was complete in 24h and the product was isolated in 98% yield, showing the present system to be more efficient than the H-b zeolite-catalytic system, 11 wherein a 97% yield was achieved in a 48h reaction. Under similar experimental conditions, 1-bromo-2-naphthol, 3 gave a 92% yield of 2, while 1-chloro-2-naphthol was un- changed. The conversion of 1-iodo-2-naphthol was higher than its bromo analogue. 10 OH OH X MeOH, reflux, 24 h 1, X = I , 98%; 3, X = Br, 92% 2 KHSO 4 -Na 2 SO 3 ð1Þ The same strategy was extended to 2,4,6-triiodophenol and 2,4,6-tribromophenol to obtain the corresponding 2,6-dihalophenol in moderate yields after 48h (Eq. 2). Keywords: KHSO 4 –Na 2 SO 3 ; Debromination; Deiodination. *Corresponding author. Tel.: +91-0278-2561354; fax: +91-0278-256- 7562; e-mail addresses: gramachandra@rediffmail.com; salt@csir. res.in 0040-4039/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2004.05.025 Tetrahedron Letters 45 (2004) 5251–5252 Tetrahedron Letters