FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(Section 10 and rule 13)
1. "An improved method for the synthesis of azobenzene from nitrobenzene and
sodium hydroxide".
2. (a) Nagarkar Jayashree Milind
Department of Chemistry, Institute of Chemical Technology, Nathalal Parekh Marg., Matunga. Mumbai 400019, Maharashtra, India. INDIAN. (b) Gund Sitaram Haribhau Department of Chemistry, Institute of Chemical Technology, Nathalal Parekh Marg., Matunga. Mumbai 400019, Maharashtra, India. INDIAN.
The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF THE INVENTION
The aromatic azo compounds are widely used as organic dyes, radical reaction initiators; indicators in chemical laboratories and drug delivery agents. Various methods were developed for the synthesis of azobenzene in last few decades the novel method for azobenzene synthesis has been studied in this invention, which deals with the synthesis of azobenzene using nitrobenzene and sodium hydroxide in presence of ethanol as a novel hydrogen source. Use of ethanol as novel hydrogen source makes this technique greener, economically cheaper and safer as compared to reported methods. This method gives 50-100% yield of corresponding azobenzene molecules with different hydrogen sources solvent
BACKGROUND OF THE INVENTION
Aromatic azobenzene compounds are important and central building blocks in the production of dyes and pigments, agrochemicals, indicators in volumetric analysis, pharmaceuticals, polymers, and also in biological systems. Many reports are available on metal catalyzed synthesis of azo compounds from nitrobenzene. Malavalli group reported (European Journal of Chemistry 2013, 4, 61-63) Mg and triethyl ammonium bromide as a hydrogen source which is convenient reagent for the reduction of aromatic nitro compounds to symmetrically substituted azo compounds. Norio group reported (Tetrahedron, 2014, 70, 2027-2033) one-pot preparation of azobenzenes from nitrobenzenes by the combination of an indium-catalyzed reductive coupling followed by oxidation. Ju Hyun Kim group reported (Advance Synthesis and Catalysis, 2012, 354, 2412-2418) ruthenium nano particle catalyzed, controlled and chemo selective hydrogenation of nitroarenes using ethanol as a hydrogen source. Srinivasa group reported (Synthetic Comm., 2003, 33, 4221-1227) Lead-catalyzed synthesis of azo compounds by ammonium acetate from aromatic nitro compounds. Sogn et al. (U.S.Pat.No.2, 645, 636) have described reduction of nitro

compounds to azo compound in presence of naphthoquinoid compound in methanol. Johnson et al. (U.S.Pat.No.2, 551, 003) have described production of azo compound by using autoclave. Lei Hu group (Chem.Commun, 2012, 48, 3445-3447) used unsupported, ultra-thin platinum nanowire as a catalyst in the presence of H2 gas for the synthesis of azo compounds. Lei Hu group reported (Org.Lett. 2011, 13, 5640-5643) a highly active nano-palladium catalyst for the preparation of aromatic azos under mild conditions. All the above reported methods gave good to better product yields as per their reaction conditions but these methods have their own limitations. Reaction conditions like requirement of high pressure, high temperature, use of flammable hydrogen gas and use of toxic reagents are some of the drawbacks of reported methods. In some cases, transition metals are used as catalysts to achieve the desired yield of the product though these transition metals are not environmentally friendly and are very expensive. In some of the methods biologically harmful by-products are formed by using various reducing agents. Therefore there is a need to develop a protocol which will overcome the above problems by avoiding use of expensive metal catalysts and toxic reagents and which will work under relatively mild reaction conditions giving significant yield of azo compounds. Herein we report an efficient, catalyst free, chemo selective route for the synthesis of aromatic azo compounds from substituted nitroarenes.
SUMMARY OF THE INVENTION:
1. This invention does not require high pressure and temperature equipments.
2. No use of flammable hydrogen gas, absence of metallic reducing agent and other additives.

3. Use of cheap and inexpensive readily available materials.
4. The reaction operation is simple and easy to handle and is suitable for large scale industrial production.
5. Ethanol as greener solvent and low cost common base NaOH to give high yield, easy separation and purification of the azo compounds.
DETAIL DESCRIPTION OF THE INVENTION:
This innovation includes the synthesis of azobenzene using nitrobenzene and sodium hydroxide (1-5 equivalents) in presence of ethanol as a hydrogen source at 40-80 °C for 5-20 h.The process of the invention is described in detail in the example given below that is presented by the way of illustration only and should not be confined to limit the scope of the present invention. In this process the azoxybenzene is produced as an intermediate which is converted to azobenzene with the small amount of aniline and sodium acetate as by-products. The yield of azobenzene and time required for reaction completion depends on the concentration of base.
EXAMPLE1: Formation of azobenzene from nitrobenzene
A mixture of nitrobenzene 123 mg (1 mmol) and sodium hydroxide (1-5 equivalents) in ethanol was stirred at 40-80°C temperature for 5-20 h, the progress of reaction which was monitored by TLC. The reaction mixture was concentrated under vacuum after completion of the reaction. The residue was taken in water and subsequently extracted in ethyl acetate (10 x 3mL) and dried over Na2SO4- The solvent was evaporated under reduced pressure to obtain product. The crude product was purified on silica gel column by using pet ether and ethyl acetate solvent system to get the pure product. Isolated yield of azobenzene is (92%) by column

chromatography. Organic extract analysed on GC and product formation is confirmed by GCMS and 1H-NMR analysis.
MS (m/z/rel.int.): 182(M+): 51(31.7), 77(100), 105(22.9), 152(5.6), 182(17.6). 1H NMR (300 MHz, CDC13): δ 7.45-7.54 (m, 6H), 7.90-7.93 (m, 4H). EXAMPLE2: Formation of 1, 2-dio-tolyIdiazene from l-methyl-2-nitro benzene
The procedure described in example 1, was repeated by replacing nitrobenzene with 1-methyls-nitrobenzene. 137 mg (1 mmol) of l-methyl-2- nitrobenzene gave 83% isolated yield of 1, 2-dio-tolyldiazene is obtained by column chromatography. Organic extract was analysed on GC and product formation is confirmed by GCMS and !H-NMR analysis.
MS (m/z/rel.int): 210(M+): 51(5.4), 65(32.8), 91(100), 119(10.5), 165(4.9), 210(24.4).
1H NMR (300 MHz, CDC13): δ 7.61 (2H, d, J = 7.7 Hz), 7.23-7.36 (6H, m), 2.73ppm (6H, s).
EXAMPLE3: Formation of 1, 2-dim-tolyIdiazene from l-methyl-3-nitrobenzene
The procedure described in example 1, was repeated by replacing nitrobenzene with 1-methyls-nitrobenzene. 137 mg (1 mmol) of l-methyl-3- nitrobenzene gave 88% isolated yield of 1, 2-dim-tolyldiazene is obtained by column chromatography. Organic extract was analysed on GC and product formation is confirmed by GCMS and ' H-NMR analysis.
MS (m/z/rel.int): 210(M+): 51(4.2), 65(31.0), 91(100), 119(15.7), 165(7.0), 210(33.5).
1H NMR (300 MHz, CDC13): δ 7.70-7.72 (4H, m), 7.37-7.39 (2H, t, J=7.9Hz), 7.28(2H, d, J=8.3Hz), 2.45ppm (6H, s).
EXAMPLE4: Formation of 1,2-dip-tolyldiazene from l-methyI-4-nitrobenzene

The procedure described in example 1, was repeated by replacing nitrobenzene with l-methyl-4-nitrobenzene. 137 mg (1 mmol) of l-methyl-4- nitrobenzene gave 87% isolated yield of 1? 2-dip-tolyldiazene is obtained by column chromatography. Organic extract was analysed on GC and product formation is confirmed by GCMS and !H-NMR analysis.
MS (m/z/rel.int): 210(M+): 51(4.8), 65(30.1), 91(100), 119(17.4), 165(5.3), 210(30.7).
1H NMR (300 MHz, CDC13): δ 2.42 (6H, s), 7.28-7.30 (4H, d, J=8.4Hz), 7.79-7.81(4H, d, J=8.4Hz).
EXAMPLE5: Formation of 1, 2-Bis (4-ethoxyphenyl)diazene from l-ethoxy-4-
nitrobenzene
The procedure described in example 1, was repeated by replacing nitrobenzene with l-ethoxy-4-nitrobenzene. 167 mg (1 mmol) of 1-ethoxy-4-nitrobenzene gave 79 % isolated yield of 1, 2-Bis (4-ethoxyphenyl)diazene is obtained by column chromatography. Organic extract was analysed on GC and product formation is confirmed by GCMS and ]H-NMR analysis.
MS (m/z/rel.int): 270(M+): 65(31.4), 77(20.0), 91(11.0), 121(100), 149(27.8), 270(48.7).
]H NMR (300 MHz, CDCI3): 8 1.4 (6H, t, J=8Hz), 4.12 (4H, q, J=8Hz), 7.0 (4H, d, J=8.9Hz), 6.85 (4H, d, J-8.9Hz).
EXAMPLE 6: Formation of 1, 2-Bis(3-fluorophenyl) diazene from l-fluoro-3-nitrobenzene
The procedure described in example 1, was repeated by replacing nitrobenzene with l-fluoro-3-nitrobenzene. 141 mg (1 mmol) of l-fluoro-3-nitrobenzene gave 84% isolated yield of 1, 2-Bis (3-fluorophenyl) diazene is obtained by column chromatography. Organic extract was analysed on GC and product formation is confirmed by GCMS and 'H-NMR analysis.
MS (m/z/rel.int.): 218(M+): 50(2.9), 69(3.7), 75(25.1), 95(100), 123(27.2), 218(33.8)

1H NMR (300 MHz, CDC13): δ 7.19-7.29 (2H, m), 7.49-7.66 (4H, m), 7.79(2H, d). EXAMPLE7: Formation of 1, 2-Bis(3-bromophenyl) diazene from l-bromo-3-nitrobenzene
The procedure described in example 1, was repeated by replacing nitrobenzene with l-bromo-3-nitrobenzene. 202 mg (1 mmol) of l-bromo-3-nitrobenzene gave 80% isolated yield of 1, 2-Bis (3-bromophenyl) diazene is obtained by column chromatography. Organic extract was analysed on GC and product formation is confirmed by GCMS and 'H-NMR analysis.
MS (m/z/rel.int): 340(M+): 50(40.1), 63(20.0), 76(77.9), 152(20.8), 155(100), 185(47.6), 338(17.6), 340(34.6).
1H NMR (300 MHz, CDC13): δ 8.09-8.05 (2H, m), 7.90 (2H, d, J=7.9Hz), 7.64 (2H, d, J=7.9Hz), 7.39-7.47 (2H,t,J=7.9Hz).
EXAMPLE8: Formation of 1, 2-Bis (2-chlorophenyl) diazene from l-chIoro-2-nitrobenzene
The procedure described in example 1, was repeated by replacing nitrobenzene with l-chloro-2-nitrobenzene. 157 mg (1 mmol) of l-chloro-2-nitrobenzene gave 85% isolated yield of 1, 2-Bis (2-chlorophenyl) diazene is obtained by column chromatography. Organic extract was analysed on GC and product formation is confirmed by GCMS and 'H-NMR analysis.
MS (m/z/rel.int.): 250(M+): 50(13.0), 75(51.8), 111(100), 113(31.5), 139(49.0), 141(15.9), 250(23.0).
1H NMR (300 MHz, CDC13): δ 7.75 (2H, d, J=7.7Hz), 7.55 (2H, d, J=7.7Hz), 7.43-7.33(4H, m). EXAMPLE9: Formation of 1, 2-Bis (3-chIorophenyl) diazene from l-chloro-3-nitrobenzene
The procedure described in example 1, was repeated by replacing nitrobenzene with l-chloro-3-nitrobenzene. 157 mg (1 mmol) of l-chloro-3-nitrobenzene gave 87% isolated yield of 1, 2-Bis

(3-chlorophenyl) diazene is obtained by column chromatography. Organic extract was analysed on GC and product formation is confirmed by GCMS and 1H-NMR analysis.
MS (m/z/rel.int.): 250(M+): 50(10.7), 75(39.6), 111(100), 113(31.1), 139(29.6), 141(9.6), 250(20.1).
1H NMR (300 MHz, CDC13): δ 7.44-7.47 (4H, m), 7.81-7.86 (2H, m), 7.88-7.91 (2H, m).
EXAMPLE10: Formation of 1,2-Bis(4-chlorophenyl)diazene from l-chIoro-4-nitrobenzene
The procedure described in example 1, was repeated by replacing nitrobenzene with l-chloro-4-nitrobenzene. 157 mg (1 mmol) of l-chloro-4-nitrobenzene gave 61% isolated yield of 1, 2-Bis (4-chlorophenyl) diazene is obtained by column chromatography. Organic extract was analysed on GC and product formation is confirmed by GCMS and 'H-NMR analysis.
MS (m/z/rel.int.): 250(M+); 50(11.0), 75(39.7), 111(100), 113(31.8), 139(37.4), 141(12.1), 250(23.3).
1H NMR (300 MHz, CDC13): δ 7.46-7.49 (4H, d, J=8.9Hz), 7.83-7.87 (4H, d, J=8.9Hz). EXAMPLE11: Formation of 1, 2-Bis (3-iodophenyl) diazene from l-iodo-3-nitrobenzene
The procedure described in example 1, was repeated by replacing nitrobenzene with l-iodo-3-nitrobenzene. 249 mg (1 mmol) of l-iodo-3-nitrobenzene gave 82% isolated yield of 1, 2-Bis (3-iodophenyl) diazene is obtained by column chromatography. Organic extract was analysed on GC and product formation is confirmed by GCMS and 'H-NMR analysis.
MS (m/z/rel.int.): 434(M+): 50(32.7), 63(12.2), 76(100), 152(13.1), 203(88.6), 231(63.8), 434(49.3).
1H NMR (300 MHz, CDC13): δ 8.26 (2H, m), 7.93 (2H, d, J=7.9Hz), 7.84 (2H, d, J=7.9Hz), 7.24-7.33 (2H, m).
EXAMPLE12: Formation of (E)-3, 3'-(diazene-1,2-diyl)dianiIine from 3-nitroaniIine

The procedure described in example 1, was repeated by replacing nitrobenzene with 3-nitroaniline. 138 mg (1 mmol) of 3-nitroaniline gave 87% isolated yield of (E)-3, 3'-(diazene-l, 2-diyl)dianiline is obtained by column chromatography. Organic extract was analysed on GC and product formation is confirmed by GCMS and *H-NMR analysis.
1H NMR (300 MHz, CDC13): δ 7.18-7.35 (6H, m), 6.77-6.84 (2H, m), 3.81(4H, s).
EXAMPLE13: Formation of (E)-5, 5'-(diazene-l, 2-diyl)bis(2-chloroaniline) from 2-chloro-5-nitroamiine
The procedure described in example 1, was repeated by replacing nitrobenzene with 2-chloro-5-nitroaniline. 172.57 mg (1 mmol) of 2-chloro-5-nitroaniline gave 86% isolated yield of (E)-5, 5'-(diazene-1, 2-diyl)bis(2-chloroaniIine) is obtained by column chromatography. Organic extract was analysed on GC and product formation is confirmed by GCMS and 1H-NMR analysis
1H NMR (300 MHz, CDC13): δ 7.34-7.40 (2H, dt, J=7.5MHz), 7.17-7.29 (2H, m), 7.04-7.10(2H, dt,J=7.5MHz),3.5(4H,s).
EXAMPLE14: Formation of azobenzene from nitrosobenzene
The procedure described in example 1, was repeated by replacing nitrobenzene with nitrosobenzene. 107 mg (1 mmol) of nitrosobenzene gave 85% isolated yield of azobenzene is obtained by column chromatography. Organic extract was analysed on GC and product formation is confirmed by GCMS and 'H-NMR analysis.
MS (m/z/rel.int): 182(M+): 51(31.7), 77(100), 105(22.9), 152(5.6), 182(17.6). 'H NMR (300 MHz, CDCI3): 5 7.45-7.54 (m, 6H), 7.90-7.93 (m, 4H).

We Claim:
1. An improved method for azobenzene synthesis from nitrobenzene and sodium hydroxide in presence of ethanol as solvent and hydrogen donor in the temperature range of 40-80 °C temperature for 5-20 h reaction time.
2. A process as claimed in claim 1, wherein nitrobenzene used are substituted nitrobenzenes and formation of symmetrical azo compounds.
3. A process as claimed in claim 1, wherein nitrobenzene used are nitrosobenzene.
4. A process as claimed in claim 1, wherein nitrobenzene used are substituted nitrosobenzenes and formation of symmetrical azo compounds.
5. A process as claimed in claim \, wherein sodium hydroxide used are potassium hydroxide.
6. A process as claimed in claim 1, wherein ethanol used are various alcohols containing alpha hydrogen atoms like methanol, propanol, butanol, pentanol, glycerol, hexanol, benzyl alcohol.
7. A process as claimed in claim 1, wherein the reaction is in the temperature range of 40-80 °C under atmospheric pressure.
8. A process as claimed in claim 1, wherein time required are selected from 5 h to 20 h.