Indian Journal of Chemical Technology Vol. 5, May 1998, pp. 172-174 • Note

Preparation ofbenzonitrile from methyl zonitrile from methyl benzoate which is formed as benzoate and catalyzed by a by-product during oxidation of Cg cut of naphtha niobium phosphatet to dimethyl terephthalate (DMT) in petrochemical Industry. Anil Wali, S Unnikrishnan, S Muthukumaru Pillai '" & S Satish Experimental Procedure Research Centre, Indian Petrochemicals Corporation Limited., Methyl benzoate (>95%) received from DMT Vadodara 391 346, India plant (IPCL) was distilled and used. NbOP04 is a commercial sample (CBMM, Brazil). SO/IZr02 Received 31 July 1997; accepted 20 February 1998 was prepared from ZrOCI2.8H20 first converting the salt into Zr(OH)4 by precipitating with NH40H, In a catalytic reaction under vapour phase, methyl washing with and drying at 100°C for 24 h. benzoate and ammonia can be converted into benzoni• 30 mL of 1 N H2S04 was then used to treat 2 g of trile as a major and as minor products over dried Zr(OH)4 followed by drying and calcining at NbOP04 and few other solid acid catalysts. 500°C. SAPO-5 was prepared by the usual hydro• thermal crystallization of a mixture of hydrated Synthesis of is an important catalytic and alumina, silica gel and phosphoric acid using industrial process 1.2. They are produced in high triethylamine as templating agent. Formation of yield by vapour phase catalytic of the product was monitored by GC (Shimadzu 0lefins3, alkanes4 and aromatics5 using multi metal 15A) analysis on OV -17 column with Flame Ioni• containing oxides. Benzonitrile, in particular, is sation Detection. The components were identified prepared by the catalytic reaction of with by comparison with authentic samples and also by N06. A method for making benzonitrile by dehy• library search during GC-MS (HP 5890 system) drogenation of the Diels-Alder adduct of butadiene analysis. and is reported? Dehydration of car• The terms conversion and selectivity are defined boxamide has been studied using a variety of as: catalysts and dehydrating agents8•9• It has also been % Conversion = Mole of ester reacted shown that benzonitrile can be synthesized from xl00/Mole of ester taken over silica gel10 and modified Si02• % Selectivity=Mole of compoundx 100/Mole A120/1 catalyst. In the present study, conversion of of ester reacted methyl benzoate to benzonitrile has been carried out with ammonia over niobium phosphate and a Representative procedure few solid acid catalysts. Efforts are made to de• 2 g of NbOP04 mixed with quartz beads was velop new applications of niobium based catalyst loaded in a tubular down-flow fixed bed reactor in the chemical industrylo.15. It is shown that com• (20 mm i.d.). The temperature was set at 350°C mercial niobium phosphate which is amorphous and the catalyst bed was heated for 3 h under N2 showed faIrly strong surface acidity and could flow (20 mUmin). "The temperature was then promote some acid-catalyzed reactions 11. But to brought down to 320°C. Methyl benzoate (3 our knowledge niobium phosphate has not been mL/h) was fed from the top using a syringe pump. prevlOusly employed to catalyze the synthesis of Equimolar quantity of NH3 (600 mLIh) and N2 benzonitrile from methyl benzoate and ammonia. (1200 mLlh) were flown on the catalyst bed. The Such a conversion offers an alternate route to ben- product coming out of the reactor was condensed by circulating chilled water (5°C). Samples were tlPCL communication No.J26 collected at 1h intervals and anaiysed. At the end * For corH;spondcl1cc of 5 h run, the COTl\'erS1Gf1 of methyl benzoate was

~ I 1111 I "I '1'11111'11 II II·fllillll'I'1 I f "1' NOTE 173

85.6% and selectivity to benzonitrile and the am• Some of the properties of the catalysts are given ides was 96% and 4% respectively. in Table 2. Selectivity to formation of 3 and 4 in• Total number of acid sites were measured by creases with increase in acidity of the solid acid NH3 adsorption method at 100°C.The surface area catalysts (Tables 1 and 2 ). and pore volume of the catalysts were measured on The advantages of heterogeneous catalysis in Sorptomatic 1900 (Carlo Erba Strumentazione) organic reactions are not only limited to easy using N2 adsorption by the BET method. The IR work-up procedures but, also often to the recy• spectral2 of pyridine adsorbed on NbOP04 was clability of the catalyst. In accordance with this measured on Nicolet-550 FTIR spectrometer. premise the reaction was run continuously over a long period (13 h). The reaction was active Results and Discussion throughout albeit, to a lesser extent after 10_h The methyl benzoate (1)-ammonia reaction was (Table 3). The selectivity to benzonitrile was con• carried out in the temperature range 320-360°C in sistent though. The above catalyst was then regen• a down-flow glass tubular reactor. However, the erated by calcination in air at 500°C and on use optimal temperature was found to be 320°C. The was found active as before. At 340°C and over 4 h catalysts that were employed in this reaction were time on stream the average % conversion of niobium phosphate (NbOP04), sulfated zirconia methyl benzoate was 81% and selectivity to ben• (SO/'/zr02) and SAPO~5 (silica-aluminium phos• zonitrile was 87%. phate). Effects of reaction temperature and methyl FTIR spectra of pyridine adsorbed NbOP04 benzoate (1) to NH3 molar ratio were studied. gave bands at 1540 cm,l and 1455 cm-l due to Typically, benzonitrile (2), (3), N• Bronsted and .Lewis acid sites. The proportion of methylbenzamide (4), benzoic acid and both the sites on NbOP04 are same. The mecha• are formed as products. From Table 1, it is clear nistic pathway envisages initial formation of ben- that niobium phosphate catalyst proffers bette con• version and selectivity of methyl benzoate to ben• volume 9.48xlO2.88x103.9xI0-41.0xlODensityAcidity0.971.248.76g/cm30.280.750.37PoreTableSurface100.2107.3-5-516.8310-5 2--Properties0.8 of catalysts zonitrile. Therefore, NbOP04 catalyst was probed moVgcm3/g HZSM-5(Si/AI=40)SO/IZr02SAPO-5 m2/garea further for its catalytic activity.NbOP04 Catalyst

eN 6 1 2 3 4

% Conversion32060.432066.432085.696.04.034050.057.375.588.6266.612.122.481.078.72.880.14.627.028.8Selectivity"28.832073.532076.034074.380.72,034084.23602.24.31340°CTemp.Molar3+4I:1:1.31:2.91:4.4I: 1.45 1I ratio% Table I-Methyl benzoate (I)-ammonia reaction •.•• NbOP04SAPO-5S042-/Zr02HZSM-5NbOP04 d NbOP04NbOP041 :NH3 Catalyst

"Temp. 320°C, 1: 3 mUh, NH3: 600 mUh, N2: 1200 mUh, catalyst amount: 2 g; '7ime on stream: 5 h CAsdetermined by GC dSi/AI =40 174 INDIAN J. CHEM. TECHNOL., MAY 1998

Table 3-Methyl benzoate (1 )-NH) reaction over NbOP04a.b

Reaction time (h): I 2 3 4 5 7 9 II 12 13 % conv. esterC 80 74 72 67 74 67 59 64 57 51

"Temp. 320°C, 1 = 2.5 mL/h, NH) = 600 mL/h, N2 = 2400 mL/h bAverage selectivity to benzonitrile 77% CAsdetermined by GC analysis

zamide, which in turn dehydrates to benzoni• 3 Chauvin A & Lefebvre G, Petrochemical processes, trile7•13• The formation of benzonitrile from the Vol 2, Ch II (Gulf Publishing Co, Paris), 1989. 4 Kim Y C, Ueda W & Mordoka Y, Appl Catal, 70 (1991) acid9•14 amides takes place over Lewis sites 189. whereas alkylation of amide to 4 is catalyzed by 5 Denton W 1& Bishop R S, ind Eng Chem, 42 (1950) 796. Bronsted acid sites14. 6 DuPont de Nemours & Co, Inc, US Pat 2,736,739, 1956. The present study shows that niobium phosphate 7 Richmond M H, Br Pat 968752, 1964. is an effective catalyst in the selective conversion 8 Friedrich K & Wallenfels K, The chemistry of cyano of methyl benzoate to benzonitrile. group (Inter Science, New York), 1970,67. 9 Rajadhayaksha R A & Joshi G W, Heterogeneous cataly• sis andfine chemicals 1l.(Elsevier Science Publishers BV, Acknowledgement Amsterdam), 1991,479. The authors wish to thank Mr. A.B. Parikh for 10 Mitchell J A & Reid E E, JAm Chem Soc, 53 (1931) 321. technical assistance and IPCL management for II Nagaian K, Kulkarni S J, Subrahmanyam M & Rama Rao encouragement. A V,Indian J Chem Technol, I (1994) 356. 12 Hanaoka T, Takenchi K, Matsuzaki T & Sugi Y, Catal References Today, 8 (1990) 123. I Sami Matar, Mirbach M J & Tayim H A , Catalysis in 13 Martin R L, Schitine W J & Castro F P, Catal Today, 5 petrochemical processes (Kluwer Academic Publishers, (1989) 483. Boston/London), 1989, 108. 14 Wali A, Unnikrishnan S, Muthukumaru Pillai S Kaushik 2 Lebedev N N, Chemistry and technology of basic organic VK & Satish S, J Catal, 173 (1998) 84. and petrochemical synthesis, Vol 1 (Mir Publishers, Mos• 15 Nagaiah K, Kulkarni S J, Subrahmanyam M & Rama Rao cow), 1984,237. A V, indian J Chem Technol, 3 (1996) 128.

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