Argon (Stranger)
04-13-03 23:42
No 426421
      Oxime Formation Comparison, Sonson  Bookmark   

I read all of patents last night from the "Oximes" thread, and in most of them the reaction is done in dH2O. No alcohol at all. In US4015011 ex.12, a heavy mol weight ketone is oximized in dH2O. In US2237365 KOH is used as the base, also in dH2O. In most of them the PH is neatralized with base 6.0-6.2. They start out with hydroxylamine/ketone aqueous mixture, and neatralize it with base to the PH 6.0-6.2.

Also, if we are talking on a slightly larger scale, cooling looks necessary for the high yielding conversion of hydroxylamine salt to NH2OH + byproduct-->oxime.

Please comparison comment to Sonson, which is below.

Why weak base?

Why not completely aqueous?

Why did he mix the base/ketone first, then neatralized with hydroxylamine?

Why did his neutralization did not go to PH6-6.2, and stayed slightly base?
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Step 1. Formation of the oxime by Sonson.

5.4g sodium acetate trihydrate and 4ml water was combined in a 50ml round-bottomed flask. The mixture was heated gently with stirring until the acetate was in solution. 20 ml MeOH was added followed with 4.5g MDP2P. To this there was added 2.3g hydroxylamine hydrochloride and the mixture was refluxed with stirring for 1.5h. After this period 10ml water was added and the heating source was removed and the mixture was allowed to cool in a waterbath with the stirring continued. After returning to room temp the flask was put in the freezer for an hour or so. The white crystalline material was filtered and washed with 50ml water (the filtrate may turn cloudy as small amounts of product crystallizes). The product was dried over magnesium perchlorate. Final weight was 4.5g (92%). Mp: 84-85C. Litt: 84-87C (H2O-EtOH)

The oxime can also be made in equally good yields with sodium carbonate as the base in 60% EtOH [3].

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I did an experiment where:

MeOH/NH2OH and 5g ketone were combined. Then the PH was adjusted to 7 with GAA. The solution was refluxed for an hour and a half, when the reflux subsided the mixture was uniform. 10ml water was added. The oxime oiled out of the solution. The mixture was allowed to come to room temp. under running water. It was put in the freezer for 1 hour. The mixture was rotorvaped to dryness, and the white oxime crystals were collected in a quantitative yeild.

I have not been able to duplicate the experiment on larger scale.