Synthesis of Naphthalenediols by Aerobic Oxidation of Diisopropylnaphthalenes Catalyzed by N‐Hydroxyphthalimide (NHPI)/α,α′‐Azobisisobutyronitrile (AIBN)

Abstract

Naphthalenediols were successfully synthesized in a one-pot reaction through the oxidation of diisopropylnaphthalenes with air catalyzed by Nhydroxyphthalimide (NHPI) combined with a,a'-azobisisobutyronitrile (AIBN) followed by decomposition with sulfuric acid. Thus, the oxidation of 2,6-diisopropylnaphthalene with air (20 atm) in the presence of AIBN (3 mol %) and NHPI (10 mol %) in CH 3 CN at 75 8C for 21 h followed by treatment with 0.3 M H 2 SO 4 gave 2,6-naphthalenediol in 92% yield.Keywords: homogeneous catalysis; hydroperoxides, N-hydroxyphthalimide; oxidation; radicals Phenols and naphthols are an important class of compounds needed for the syntheses of dyes, pharmaceuticals and polymers. In particular, naphthalenediols are essential components of intelligent polymers such as engineering plastics and liquid crystalline polymers. 2,6-Naphthalenediol (2) has attracted much attention for its chemical and physical properties as a liquid crystalline monomer material. A classical process for the production of 2 is based on the sulfonation of naphthalene followed by alkali fusion of the resulting sulfonates.[1]However, 2 is difficult to synthesize in high yield by this method, which results in a complex mixture of several sulfonated products. It has been reported that the reaction of b-naphthol with hydrogen peroxide in the presence of a Lewis acid like SbF 5 produces 2, but this method also brings about a mixture of several regioisomeric naphthalenediols.[2] There have been several patents on the synthesis of 2 by the oxidation of 2,6-diisopropylnaphthalene (1) followed by treatment of the resulting 2,6-bis(2-hydroxy-2-propyl)naphthalene with H 2 O 2 and H 2 SO 4 .[3]The phenol synthesis through cumene hydroperoxide obtained by the aerobic oxidation of isopropylbenzene is well known as the Hock process. Recently, this methodology was applied to the synthesis of 2,6-bis(1-hydroperoxy-1-methylethyl)naphthalene (4) and 2-isopropyl-6-(1-hydroperoxy-1-methylethyl)naphthalene (5).[4] In a previous paper, we have reported the aerobic oxidation of methylbenzenes like toluene and xylene to the corresponding carboxylic acids using N-hydroxyphthalimide (NHPI) as a key catalyst.[5] In addition, we reported the epoxidation of olefins with ethylbenzene hydroperoxide, generated in situ from the aerobic oxidation of ethylbenzene by NHPI, in the presence of Mo(CO) 6.[6] This fact shows that the NHPI-catalyzed oxidation of alkylbenzenes can be applied to the synthesis of alkyl hydroperoxides from alkylbenzenes. [7] ly, Sheldon et al. have reported phenol synthesis by means of the NHPI-catalyzed aerobic oxidation of cyclohexylbenzene. [8] We now report an efficient synthesis of naphthalenediols via aerobic oxidation of diisopropylnaphthalenes catalyzed by NHPI and AIBN.The aerobic oxidation of 1 was chosen as a model reaction and was carried out in the presence of catalytic amounts of AIBN and NHPI under various conditions (Table 1). 1Compound 1 was allowed to react under O 2 (1 atm) in the presence of AIBN (3 mol %) an...

Metal-free aerobic oxidations mediated by N-hydroxyphthalimide. A concise review

“…For example, the oxidation of 2,6-diisopropylnaphthalene with air in the presence of α,α’-azobisisobutyronitrile (AIBN) and NHPI, followed by decomposition with sulfuric acid of the dihydroperoxide oxidation product, gave the corresponding 2,6-naphthalenediol in 92% yield (Scheme 3) [16]. …”

Improvement the Activity and Selectivity of Fenton System in the Oxidation of Alcohols

“…Therefore, we believed that there should be at least two ways to improve reaction selectivity of Fenton system. One is to control the generation rate of hydroxyl radicals, and the other is to reduce the accumulation of nonselective hydroxyl radicals and convert them to radicals with higher selectivity, such as phthalimide N-oxyl (PINO), which has been widely used in oxidation reaction [32][33][34][35]. Adding inorganic buffers can change the pH of reaction mixture and control the generation rate of radicals.…”

“…There are two keys to successfully develop this method: first, the additive should mainly exist in the organic phase, which can avoid possible influence on the Fenton system induced by the additive; second, the additive can react with hydroxyl radicals to generate other radicals with high oxidation selectivity quickly (Figure 1). N-Hydroxyphthalimide (NHPI) is an excellent choice under these two restrictions, and PINO radical can be generated from NHPI, which has been proven to be catalyst with high oxidation selectivity [32][33][34][35]. Then, the effect of NHPI as additive was studied.…”

Gold Nanoparticle–Polydopamine–Reduced Graphene Oxide Ternary Nanocomposite as an Efficient Catalyst for Selective Oxidation of Benzylic C(sp3)−H Bonds Under Mild Conditions

“…Ishii and co-workers showedt hat ac ombination of NHPI with transition metals,n otably cobalt (known as the Ishii system), or with polyoxometalates gives an excellent catalytic system for the autoxidation of ab road range of organics ubstrates. [14] Even non-metallicc ompounds such as alkyl hydroperoxides, [15] a,a-azobisisobutyronitrile, [16] aldehydes, [17] and NO 2 [18] have been used as mediators for NHPI-basedo xidation. The biomimeticc atalytic system involving anthraquinone derivatives, zeolites, andN HPIh as also shown superior activity towards CÀHo xygenation of hydrocarbons.…”