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pip
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[*] posted on 19-9-2008 at 16:27
benzophenone synthesis


i used the fse all i could but i could not find a synthesis for 2-amino-5 chloro-benzophenone but i did find one for 2-amino-5-nitro-benzophenone so i am asking if i could subsitute the following chems 4-nitroaniline for 4-chloroaniline and get what i am looking for. the synthesis is:

Presynthesis (95% yield) is necessary: N-benzoyl-4-nitroaniline
Dissolve 138 g (1 mole) 4-nitroaniline in 1 l dry pyridine and add dropwise with ice-coling - internal temp below 20°C - 141 g (1.01 mole) benzoyl chloride over 2 h. Stir at 30°C 24 h and evaporate to dryness at the rotovap in vacuo. Recover the expensive dist-off pyridine! The rest is suspended in 1 L 40°C water and the product filtered and water-washed to remove pyridine rests. The mass is suspended in a 2 L flask in 500 mL toluene, a water-trap and a reflux condenser are attached and the mixture refluxed to remove any water, then the toluene is distilled off in vacuo (recover) and then, it is dried at 80°C in vacuo and weighed (weigh the flask before and after). The yield is about 242 g N-benzoyl-4-nitroaniline.

2-amino-5-nitro-benzophenone - DDR (GDR) patent 74798
Now example 1:

In the 2l-flask, mix 242 g N-benzoyl-4-nitroaniline, 280 mL benzoyl chloride and 200 g fresh dry zinc chloride. Add a reflux condenser and stirr under moisture protection at 170°C internal temp (exact 165-175°C) for 9 h while HCl gas is evolved.
After cooling down to 120°C, 1 l water is added dropwise (vigorous reaction), with stirring, and at 60°C, the granular mass is suction filtered and washed, succed dry. 286 mL conc. sulfuric acid is added to 150 mL water and the dry product (N-benzoyl-2-amino-5-nitro-benzophenone) and the whole is stirred for 40 min. at 140-150°C (do not change). Immediately, it is poured in 1/2 l water. After cooling to RT, the precipitate is suction-filtered and water-washed, then the crude product is stirred with 750 mL 10% sodium hydroxide for 2 h. (removes benzoic acid) Then, the purified product is suction-filtered, water-washed, succed dry and dried at 80°C in vacuum. Yield 90 g, that is 37%. mp 154-160°C, 92-95% pure.

[Edited on 19-9-2008 by pip]
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Nicodem
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[*] posted on 22-9-2008 at 00:36


Are you looking for a preparation of benzophenone if I understood well? The preparation of substituted benzophenone that you cited will not work for benzoyl chloride and benzene. Firstly, because you can obviously not achieve such temperatures with benzene and PhCOCl. Nevertheless, in the literature you can find numerous examples using all kind of acids. A paper even claims zinc oxide works for this reaction (J. Org. Chem., 69, 6953-6956 which was already uploaded on the forum somewhere), so I would not be surprised if ZnCl2 would work under certain conditions. FeCl3 was also reported to work at high temperatures (Industrial & Engineering Chemistry Research, 39, 1124-1131).
Anyway, there are numerous examples in the literature, you just did not search for it, or maybe you did not search the right places. Try chemical journals instead of patents, or laboratory manuals such as Organikum, Vogel's, etc...




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[*] posted on 22-9-2008 at 02:16


I think he is trying to make 2-amino-5-chlorobenzophenone following a procedure for 2-amino-5-nitrobenzophenone. Looking at it quickly, I would say that if you used 4-chloroaniline that it should work.



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[*] posted on 22-9-2008 at 23:15


Quote:
Originally posted by pip
i could not find a synthesis for 2-amino-5 chloro-benzophenone but i did find one for 2-amino-5-nitro-benzophenone so i am asking if i could subsitute the following chems 4-nitroaniline for 4-chloroaniline and get what i am looking for. the synthesis is:

Sorry, I read to fast and misunderstood the above and thought you wanted to prepare plain benzophenone. Should not read the posts too early in the morning. I agree with Paziandi, the reaction should proceed with 4-chloroaniline just as well (provided you recalculate the masses). 4-Chlorobenzanilide is considerably more nucleophilic than 4-nitrobenzanilide, so perhaps you will get some side reactions. In such a case try again with reduced reaction temperature.




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panziandi
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[*] posted on 23-9-2008 at 07:55


Yes I was thinking about the likelihood of side reactions especially as these Friedle-Crafts reactions favour multiple substitutions. Reducing quantity of alkylating reagent and using an excess of the arene tends to be useful. ofcourse the 2-amino-5-chlorobenzophenone is already quite hindered on the main ring. Certainly a reduction in reaction temperature would lower side reactions if they are a problem.



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[*] posted on 23-9-2008 at 14:03


It's an Friedel-Crafts acylation (not alkylation) and (unlike polyalkylation) the polyacylation is not something that happen likely.



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