Nitration of benzene

Abstract

The present invention discloses a process for nitration of benzene. More particularly, the present invention discloses an efficient, environmental friendly process for the nitration of benzene using a modified solid acid catalyst.

Claims

1. A benzene nitration catalyst comprising hydrophobic solid acid WO.sub.3/SiO.sub.2 grafted with an organosilane selected from a C2 to C10 alkyl trialkoxysilane.

2. The benzene nitration catalyst of claim 1, wherein the alkoxy in the C2 to C10 alkyl trialkoxysilane is methoxy, ethoxy or propoxy.

3. A process for preparing a benzene nitration catalyst comprising the steps of: a. dispersing 20% WO.sub.3/SiO.sub.2 in dry toluene to form a mixture: b. adding an organosilane selected from an alkyl trialkoxysilane to the mixture of step a; c. heating the resultant mixture of step b with constant mixing to obtain a powder and d. drying the resultant powder of step c to obtain the benzene nitration catalyst.

4. The process of claim 3, wherein the a ratio of WO.sub.3/SiO.sub.2 to the dry toluene is 1:4 to 1:20.

5. The process of claim 3, wherein the benzene nitration catalyst is-comprises solid WO.sub.3/SiO.sub.2 grafted with the organosilanes.

6. The process of claim 3, wherein in step d, the resultant powder of step c is dried in an oven.

7. A process for nitration of benzene comprising the steps of: a) charging benzene and a grafted hydrophobic solid acid catalyst in the range of 1:0.1 to 1:1 in a reactor flushed with nitrogen to form a reaction mixture followed by refluxing the reaction mixture at a temperature in the range of 90 to 110° C. for a period in the range of 1 to 2 hour and b) adding nitric acid to the reaction mixture of step (a) with constantly removing by azeotropic distillation of the water formed followed by refluxing the resultant reaction mixture at a temperature in the range of 90 to 110° C. for a period in the range of 6 to 8 hour to form a mononitrobenzene.

8. The process of claim 7, wherein the hydrophobic solid acid catalyst is WO.sub.3/SiO.sub.2.

9. The process of claim 7, wherein conversion of the benzene to the mononitrobenzene is in the range of 50 to 100%.

10. The process of claim 7, wherein selectivity of forming the mononitrobenzene is 100%.

11. The process of claim 7, wherein the grafted hydrophobic solid acid catalyst does not get deactivated during the nitration of benzene and is recycled.

12. The process of claim 7, wherein the grafted hydrophobic solid acid catalyst comprises hydrophobic solid acid WO.sub.3/SiO.sub.2 grafted with an organosilane.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1: XRD pattern of catalyst prepared in example 3

(2) FIG. 2: FTIR spectra of catalyst prepared in example 3

(3) FIG. 3: NH.sub.3-TPD of catalyst prepared in example 3

(4) FIG. 4: BET surface analysis of catalyst prepared in example 3

(5) FIG. 5: Pore size distribution of catalyst prepared in example 3

DETAILED DESCRIPTION OF THE INVENTION

(6) The invention will now be described in detail in connection with certain preferred and optional embodiments, so that various aspects thereof may be more fully understood and appreciated.

(7) The present invention provides a process for nitration of benzene and grafted hydrophobic solid acid catalyst for use in nitration of benzene.

(8) In an embodiment, the present invention provides a process for nitration of benzene comprising the steps of: a) charging benzene and a grafted hydrophobic solid acid catalyst in the range of 1:0.1 to 1:1 in a reactor flushed with nitrogen followed by refluxing the reaction mixture at temperature in the range of 90 to 110° C. for the period in the range of 1 to 2 hour and b) adding nitric acid to the reaction mixture of step (a) with constantly removing the water formed by azeotropic distillation followed by refluxing the reaction mixture at temperature in the range of 90 to 110° C. for the period in the range of 6 to 8 hour to afford mononitrobenzene.

(9) In a preferred embodiment, the solid acid catalyst is, WO.sub.3/SiO.sub.2 catalyst which is post grafted with commercial organosilanes.

(10) The conversion of benzene is in the range of 50 to 100%.

(11) The selectivity of said reaction towards mononitrobenzene is 100%.

(12) To prevent the deactivation of the catalyst during the nitration process of benzene, the inventor discloses a process to make the catalyst of the invention hydrophobic. The grafted hydrophobic solid acid catalyst is disclosed with high activity for liquid phase nitration of benzene. The nitration of benzene has been carried out using commercial 70% nitric acid without using any solvent. The HNO.sub.3 conversion obtained is 80-85% with recovery of remaining 20-15% HNO.sub.3. The catalyst is recycled efficiently.

(13) In another embodiment, the present invention provides a grafted hydrophobic solid acid catalyst that does not get deactivated during the nitration of benzene.

(14) In a preferred embodiment, the grafted hydrophobic solid acid catalyst is WO.sub.3/SiO.sub.2 grafted with alkyl triethoxysilane.

(15) In prior art, unmodified WO.sub.3/SiO.sub.2 catalyst is used but in preset invention to use additional solvent (ethylene dichloride) for removal of water. Without the additional solvents the reaction is not effective due to hydrophilic nature of the catalyst. Whereas in present invention when the catalyst is modified to make it more hydrophobic, no need of additional solvent for removal of water. In the present disclosure simple HNO.sub.3 (65-70%) is used for nitration which is very safe for handling. This does not need high pressure autoclave for reaction. Reaction is carried out in simple glass vessel.

(16) The WO.sub.3/SiO.sub.2 catalyst is post grafted with commercial organosilane to make it hydrophobic. The organosilane used to improve the hydrophobic nature of the catalyst is Dynasylan 9896. The ethoxy groups of alkyl triethoxysilane reacts with surface Si—OH to form covalent Si—O—Si bond upon hydrolysis.

(17) The powder X-ray diffraction patterns of the catalysts were recorded on PAN anlyticalX'Pert Pro Dual Goniometer diffractometerX'celerator solid state detector was employed for the experiments with CuKα (1.542 Å) radiation and a Ni filter (FIG. 1). The PXRD patterns of the catalyst synthesized in example 3 shown in FIG. 1. The XRD patterns exhibited sharp peaks corresponding to monoclinic WO.sub.3 phase at 23.2°, 23.6°, 24.2°, 26.6°, 28.8° and 33.5° corresponding to (002), (020), (220) and (202) planes of monoclinic crystalline WO.sub.3 phase (JCPDS No. 43-1035) on the broad underlying peak characteristic of the amorphous silica at 2θ=24°. It is observed that monoclinic phase of WO.sub.3 is unaltered.

(18) The Fourier transform infrared (FT-IR) spectra of the samples are recorded on a Thermo Nicolet Nexus 670 IR instrument at ambient conditions using KBr pellets with a resolution of 4 cm.sup.−1 in the range of 4000-400 cm.sup.−1 averaged over 100 scans. KBR pelleted FTIR spectrum of catalyst synthesized in example 3 is presented in FIG. 2. The prominent bands around 1300-1000 cm.sup.−1 could be assigned to the asymmetric, symmetric stretching and bending vibrations of Si—O—Si, respectively whereas the bands at 942 and 802 cm.sup.−1 were due to the W═O.sub.t and W—O—W stretching vibrations, respectively. The IR band at 468 cm.sup.−1 is due to O—Si—O bending vibrations. The bands in the region of 2800-3100 cm.sup.−1 were attributed to the C—H stretching vibrations of —CH.sub.2 and —CH.sub.3 groups from alkyl triethoxysilane grafted on SiO.sub.2.

(19) The ammonia-TPD experiments are carried out to determine the acid strength of the catalyst synthesized in example 3 is shown in FIG. 3. The ammonia desorption curve of example 3 indicated presence of maximum number of medium and weak acid sites (150-350° C.) with total acidity of 0.54 mmol/g.

(20) The surface analysis of catalyst synthesized in example 3 was carried out using BET method and results are shown in Table 1. A very high surface area of 302 m.sup.2/g was observed for example 3 because of sol-gel technique using ES-40 as the silica source. The total pore volume is 0.33 cc/g, with pore size 20.5 Å (FIG. 4).

EXAMPLES

(21) Following examples are given by way of illustration therefore should not be construed to limit the scope of the invention.

Example 1: Catalyst Preparation

(22) In a 50 mL beaker, 4.25 g ammonium metatungstate was dissolved in 10 mL distilled water. In another 250 mL beaker, a solution of 40 g ethyl silicate-40 and 30 g iso-propyl alcohol was stirred for 1 h and to this solution aqueous solution of ammonium metatungstate was added drop wise. This solution was stirred for 3 h followed by addition of 2 mL 2.5% aqueous ammonia solution. The solution was stirred until a white colored gel was obtained. This gel was air dried and calcined at 500° C. for 5 h to obtain 20% WO.sub.3/SiO.sub.2 catalyst.

Example 2: Synthesis of Modified Catalyst

(23) In a typical procedure, 5.0 g 20% WO.sub.3/SiO.sub.2 catalyst as prepared in Example 1, was dispersed in 25 mL dry toluene. To this solution 0.08 g of alkyl triethoxysilane (Dynasylan 9896) was added and the resultant mixture was heated at 80° C. with constant mixing on rotary evaporator for 8 h. Then toluene was evaporated under vacuum and resultant powder was dried in oven at 100° C. for 5 hrs.

Example 3: Synthesis of Modified Catalyst

(24) In a typical procedure, 5.0 g 20% WO.sub.3/SiO.sub.2 catalyst as prepared in Example 1, was dispersed in 100 mL dry toluene. To this solution 0.265 g of alkyl triethoxysilane (Dynasylan 9896) was added and the resultant mixture was heated at 80° C. with constant mixing on rotary evaporator for 8 h. Then toluene was evaporated under vacuum and resultant powder was dried in oven at 100° C. for 5 hrs.

Example 4: Synthesis of Modified Catalyst

(25) In a typical procedure, 5.0 g 20% WO.sub.3/SiO.sub.2 catalyst as prepared in Example 1, was dispersed in 100 mL dry toluene. To this solution 0.4 g of alkyl triethoxysilane (Dynasylan 9896) was added and the resultant mixture was heated at 80° C. with constant mixing on rotary evaporator for 8 h. Then toluene was evaporated under vacuum and resultant powder was dried in oven at 100° C. for 5 hrs.

Example 5: BET Surface Analysis

(26) The BET surface area of the calcined samples was determined by N.sub.2 sorption at −196° C. using NOVA 1200 (Quanta Chrome) equipment. Prior to N.sub.2 adsorption, the materials were evacuated at 300° C. under vacuum. The specific surface area, BET, was determined according to the BET equation.

(27) TABLE-US-00001 TABLE 1 Surface analysis and acidity of the catalysts Surface Pore Pore NH.sub.3 area volume radius desorbed Sample m.sup.2/g cc/g Å mmol/g Catalyst as in 302 0.33 20.5 0.54 Example 3

Example 6: NH.SUB.3.-TPD Experiment

(28) The NH.sub.3-TPD experiments were performed using a Micromeritics Autochem 2910 instrument. A weighed amount of the sample (˜100 mg) was placed in a quartz reactor, pretreated in a flow of helium gas at 500° C. for 1 h (ramp rate of 10° C.min.sup.−1) and cooled to 100° C. The catalyst was then exposed to NH.sub.3 gas (5% NH.sub.3-95% He, 50 mLmin.sup.−1) at 100° C., followed by evacuation at 100° C. for 3 h. Then, the desorbed NH.sub.3 was measured from 100° C. to 700° C. with a heating rate of 5° C.min.sup.−1 in flow of helium as a carrier gas at a flow rate of 60 mLmin.sup.−1 until ammonia was desorbed completely. Ammonia-TPD experiments were carried out to determine the acid strength of the catalyst synthesized in example 3 is shown in FIG. 3. The ammonia desorption curve of example 3 indicated presence of maximum number of medium and weak acid sites (150-350° C.) with total acidity of 0.54 mmol/g.

Example 7: Nitration of Benzene

(29) A 250 mL three-necked round bottom flask fitted with Dean-Stark apparatus was charged with 100 g benzene and 10 g catalyst as prepared in example 2. The flask was flushed with nitrogen. The solution was refluxed at 90° C. for 1 h. Then 61.7 mL of 70% HNO.sub.3 was added to the reaction flask dropwise. The water formed during the reaction was removed azeotropically using the Dean-Stark apparatus. The reaction was carried out for 8 h. The reaction was monitored by GC analysis. In this reaction 50% conversion of benzene was obtained with 100% selectivity for mononitrobenzene.

Example 8: Nitration of Benzene

(30) A 250 mL three-necked round bottom flask fitted with Dean-Stark apparatus was charged with 100 g benzene and 10 g catalyst as prepared in example 3. The flask was flushed with nitrogen. The solution was refluxed at 90° C. for 1 h. Then 61.7 mL of 70% HNO.sub.3 was added to the reaction flask dropwise. The water formed during the reaction was removed azeotropically using the Dean-Stark apparatus. The reaction was carried out for 8 h. The reaction was monitored by GC analysis. In this reaction 60% conversion of benzene was obtained with 100% selectivity for mononitrobenzene.

Example 9: Nitration of Benzene

(31) A 250 mL three-necked round bottom flask fitted with Dean-Stark apparatus was charged with 100 g benzene (1.28 mol) and 10 g catalyst as prepared in example 4. The flask was flushed with nitrogen. The solution was refluxed at 90° C. for 1 h. Then 61.7 mL of 70% HNO.sub.3 was added to the reaction flask dropwise. The water formed during the reaction was removed azeotropically using the Dean-Stark apparatus. The reaction was carried out for 8 h. The reaction was monitored by GC analysis. In this reaction 46% conversion of benzene was obtained with 100% selectivity for mononitrobenzene.

Example 10: Nitration of Benzene

(32) A 250 mL three-necked round bottom flask fitted with Dean-Stark apparatus was charged with 100 g benzene and 10 g catalyst as prepared in example 3. The flask was flushed with nitrogen. The solution was refluxed at 90° C. for 1 h. Then 93.1 mL of 50% HNO.sub.3 was added to the reaction flask dropwise. The water formed during the reaction was removed azeotropically using the Dean-Stark apparatus. The reaction was carried out for 8 h. The reaction was monitored by GC analysis. In this reaction 30% conversion of benzene was obtained with 100% selectivity for mononitrobenzene.

Example 11: Nitration of Benzene

(33) A 250 mL three-necked round bottom flask fitted with Dean-Stark apparatus was charged with 62.4 g benzene and 2.88 g catalyst as prepared in example 3. The flask was flushed with nitrogen. The solution was refluxed at 90° C. for 1 h. Then 7.6 mL of 90% HNO.sub.3 was added to the reaction flask dropwise. The water formed during the reaction was removed azeotropically using the Dean-Stark apparatus. The reaction was carried out for 8 h. The reaction was monitored by GC analysis. In this reaction 40% conversion of benzene was obtained with 100% selectivity for nitrobenzene.

Example 12: Nitration of Benzene

(34) A 250 mL three-necked round bottom flask fitted with Dean-Stark apparatus was charged with 100 g benzene and 10 g catalyst as prepared in example 2. The flask was flushed with nitrogen. The solution was refluxed at 110° C. for 1 h. Then 61.7 mL of 70% HNO.sub.3 was added to the reaction flask dropwise. The water formed during the reaction was removed azeotropically using the Dean-Stark apparatus. The reaction was carried out for 8 h at 110° C. The reaction was monitored by GC analysis. In this reaction 45% conversion of benzene was obtained with 100% selectivity for mononitrobenzene.

Example 13: Catalyst Recycle Study

(35) A 250 mL three-necked round bottom flask fitted with Dean-Stark apparatus was charged with 100 g benzene and 10 g catalyst as prepared in example 3. The flask was flushed with nitrogen. The solution was refluxed at 90° C. for 1 h. Then 61.7 mL of 70% HNO.sub.3 was added to the reaction flask dropwise. The water formed during the reaction was removed azeotropically using the Dean-Stark apparatus. The reaction was carried out for 8 h. The reaction was monitored by GC analysis. In this reaction 60% conversion of benzene was obtained with 100% selectivity for mononitrobenzene. After completion of reaction the reaction mixture was decanted leaving behind the catalyst in the flask and to the same flask fresh charge was added. Similarly such 4 recycles were carried out and the conversion and selectivity in each cycle is given below:

(36) TABLE-US-00002 TABLE 2 Catalyst Recycle study Sr. Recycle Benzene Nitrobenzene No. no. Conversion, % selectivity % 1 0 60 100 2 1 60 100 3 2 58 100 4 3 61 100 5 4 59 100

Advantages of the Invention

(37) 1) No use of sulphuric acid and hence no formation of byproduct waste. Environmentally benign process. 2) No use of conc. sulphuric acid and fuming nitric acid, hence no use of costly material of construction for the process plant. 3) A new composition of hydrophobic WO.sub.3/SiO.sub.2 quite active and selective for liquid phase nitration of benzene. 4) Catalyst successfully recycled up to 4 cycles without losing its activity. 5) Commercial nitric acid of 65-70% concentration can be used for nitration reaction, hence less handling hazards as well as lower cost.