A unique product of 1;2 Shift, Beckmann reaction has it’s good many synthesis application. Beckmann reaction is a general tool in organic chemistry. The reaction requires high reaction temperature; strong acidic conditions and dehydrating media.1,2 Amides are important biological and commercial compounds. Because amide constitutes the backbone of protein molecules, their chemistry is of extreme importance. The penicillin and cephalosporin antibiotics are among the best-known products of the pharmaceutical industry.3 Keep all such things in mind we go for preparation of anilides, which also contribute excellent role to synthesis, various organic compounds.
The Beckmann rearrangement requires strong acidic conditions such as conc. Sulphuric acid or Phosphoric acid these have a large amount of side products and serious corrosion problems. So, In recent days the milder conditions were tried and investigated on clean, simple, ecofriendly benign and excellent process became the chemists interesting undertaking.4,5 Several improved or developed process are reported using modified reagents6 and solid acid catalyst like clay,7 zeolites8 and silica sulfuric acid.8(c) However, the reactions are sluggish when they are performed in the liquid phase.5-8,10 Relatively few solid phase methods have been developed.11 Also the Beckman reaction using a Stoichiometic amount of cynuric chloride and Dimethyl formamide salt, Reactions was observed with solvents other than Dimethyl formamide and the reaction rate decreased noticeably with a reduced amount of cyanuric chloride in Dimethyl formamide.9
Also some methods are available for one-pot Beckmann reaction of Acetophenone (ketone).12-15 Hence, overcome all such disadvantages we report clean, effective, and simple method for one-pot synthesis of anilides in presence of catalytic amount of silica supported Sulphamic acid using microwave irradiation under solvent free condition.
RESULTS AND DISCUSION
Silica supported Sulphamic acid is an excellent mild catalyst over Sulphuric acid and Chlorosulphonic acid16 in organic reactions without any limitations such as use of rather toxic, harmful solvents and expensive reagents. Hence, we tries mild acid catalyst Sulphamic acid17 which shows rather slow rate of reaction and lower yield, therefore on using solid support (silica), which gives enhancement in the rate of reaction and better yields. Reaction goes through simple, clean and environmental friendly.
To prepare anilides various acetophenones (ketones) were mixed with hydroxyl amine hydrochloride and Silica-Sulphamic acid using mortar and pestle. The reaction mixture was irradiated in microwave oven for 7-15 min. The Corresponding anilides was obtained in excellent yield. The experimental results are summarized in Table 1.
As Shown in Table 1 several structurally varied acetophenones undergo clean, remarkably fast and direct nitrogen insertion by a one pot Beckmann type reaction to the corresponding anilides. This simple, clean, mild acid catalyst use for prepare different anilides. In Table 2 shows correlation between Sulphamic acid and silica supported Sulphamic acid for the model reaction, we examine three different derivatives and observed there is better result for reaction time and yield using silica supported Sulphamic acid catalyst.
Table 1.aProducts yield are isolated yield.
Table 2.Correlation between Sulphamic acid and Silica-Sulphamic acid catalyzed reaction
In conclusion, a green benign method for synthesis of anilides has been developed with easy workup, high selectivity, without formation of bi-products such as tetrazole, amino tetrazoles, nitriles, ureas, etc.
Melting points were uncorrected and recorded in open capillary. IR spectra were recorded on FT/IR-410 type(A) spectrophotometer in KBr. 1HNMR spectra were measured in DMSO-d6 solution on a Bruker spectrophotometer at 400 MHz. Silica gel 60(230-400 mesh) was purchased from fluka and was dried in an oven at 120℃ for 2 h.
Preparation of silica supported Sulphamic acid: For this preparation Silica gel (230-400 mesh) about 0.5 gm with 1mmole of Sulphamic acid (0.96 gm) was taken and mill that mixture for few minutes by using mortar and piston at room temperature. The mixture of Silica -Sulphamic acid used for further reaction.
General procedure: A mixture of acetophenone (2 mmol), Hydroxyl amine hydrochloride (4 mmol) and Silica-Sulphamic acid (1.96 gm) was grounded in mortar and reaction mixture was irradiated in domestic microwave oven at 450 W for optimized time indicated in Table 1. The progress of reaction monitored by TLC. After the completion of reaction, reaction mass dissolved in dichloromethane and catalyst was separated by filtration and product washed by water and dried over sodium Sulphate and solvent evaporated in vacuum to obtained crude product. The purification of crude product done by recrystallization in ethanol. Products are known compounds and were characterized by comparison of their spectral data (IR, 1HNMR) and physical properties.
Compound (4) 1HNMR (DMSO; d6) 2.0 ppm (s, 3H), 4.0 ppm (q, 2H), 1.3 ppm (t, 3H), 6.8 ppm (d, 2H), 7.8 ppm(d, 2H), 9.8 ppm (s, 1H). IR (KBR): 3300cm-1, 1670 cm-1.
Compound (12) 1HNMR (DMSO; d6) 2.0 ppm (s, 3H), 7-7.6 ppm (m, 4H), 9.4 ppm (s, 1H). IR (KBR): 3250 cm-1, 1665 cm-1.