Problem with P2P synthesis via acylation of PAA of CaOAc.

tetraedr · Mon Mar 14, 2005 7:40 pm

My Dead Ass did this reaction several times. In (about) of 100 g of PAA (and 300 g of lead acetate) scale. The yields were about 30-40 g of P2P from 100 g of PAA.

This procedure is described in Rhodium Chhmistry Archive.
But in the same place is noticed, that using Calcium Acetate instead Lead also possible. My Dead Ass did this reaction... But it is NOT WORKING!!! No reaction! Only water with AcOH were distilled from flask at the same conditions, as for lead aceatate (first, My Dead Ass melted this mixture at normal pressure, then attempted to distill the P2P, as usually). Attempt was failed.

In present My Dead Ass trying to recover some amount PAA from wihe solid. It seems so hard....

brain · Linguist Extraordinaire

I recovered 15g p2p from 100g paa... with caoac ;/ ... caoca-is shit Smile

try feoac !! yelds much higher (byt must to dry,,, ! feoac forst)

java · Consumer

Here is the original method for making p2p as it is calle d the dakin west reaction.....and some of its variations , which may be of some help to you in your dreams..........java

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Rhodium
(Chief Bee)
04-27-04 22:33
No 503369
Review: The Dakin-West Reaction
(Rated as: good read)

Review: The Dakin-West Reaction
Buchanan, G.L.
Chem. Soc. Rev. 17, 91-109 (1988) (https://www.rhodium.ws/pdf/dakin-west.review.pdf)

This is the reaction mechanism of the classic P2P synthesis which involves reflux of a mixture of phenylacetic acid, acetic anhydride and a weak base (often sodium acetate or pyridine).
The Hive - Clandestine Chemists Without Borders

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Rhodium
(Chief Bee)
06-16-04 00:48
No 513650
More on the Dakin-West reaction
(Rated as: good read)

The Conversion of Arylacetic Acids into Ketones
G. L. Buchanan and J. McArdle
J. Chem. Soc. 2944-2945 (1952) (https://www.rhodium.ws/chemistry/dakin-west.mechanism.html)

The reaction between phenylacetic acid and acetic anhydride in the presence of pyridine was originally described by Dakin and West (J. Biol. Chem. 78, 91 (1928) (http://www.jbc.org/cgi/reprint/78/1/91)) who noted that the main product was benzyl methyl ketone. King and McMillan (J. Amer. Chem. Soc. 73, 4911 (1951) (https://www.rhodium.ws/pdf/decarboxylative.arylacetic.acylation.pdf)) have re-investigated this reaction and shown that dibenzyl ketone is also formed. They consider the reaction to be a "base-catalysed condensation reaction of two acid anhydride molecules", and propose the above mechanism.

[image]

We were also engaged on this same problem, and our results are very similar. We agree that the reaction is essentially that of an acid anhydride in the presence of a base, but disagree with the mechanism proposed for these reasons. If the reaction is a condensation reaction as shown above, the essential step is the acylation of the reactive methylene group by a molecule of anhydride. It would therefore be expected that the similarly active methylene group of phenylacetic ester would be acylated under the reaction conditions, yielding ethyl α-phenylacetoacetate. This, we find does not take place. Even the more reactive benzyl cyanide, which would be expected to yield α-acetylbenzyl cyanide, fails to react, and in each case the starting material was recovered in almost quantitative yield. Moreover, such a mechanism assumes that a β-keto-acid anhydride will readily lose carbon dioxide, although it is known that at least one such substance (I) (Schinz and Hinder, Helv. Chim. Acta, 1947, 30, 1372) is relatively stable.

[image]

We envisage a migration mechanism as the only one which satisfactorily accounts for all the facts:

[image]

The rearrangement step finds a parallel in the O → C migration of the acyl group in acylated β-keto-esters (Claisen, Ber., 1900, 33, 3778). It is also possible that the recently reported rearrangement of the enol acetates of ketones (Hauser et al., J. Amer. Chem. Soc., 1950, 72, 3635) represents a less favourably activated example of the same reaction.

Experimental

Ethyl phenylacetate (45 g) was refluxed for 20 hours with acetic anhydride (125 mL) and dry pyridine (125 mL). The anhydride and pyridine were then removed in vacuo and the residual liquid fractionated. The product (43 g), bp 115°C/15 mm., gave an amide, mp 157°C not depressed on admixture of the specimen with an authentic sample of phenylacetamide.

Benzyl cyanide (30 g.) was refluxed for 9 hours with acetic anhydride (100 mL.) and dry pyridine (100 mL.), and then worked up as before. The product (27 g.), bp 108°C/15 mm., gave a benzylidene derivative, mp 86°C, not depressed on admixture of the specimen with α-cyanostilbene.
The Hive - Clandestine Chemists Without Borders

tetraedr · Mon Mar 14, 2005 11:02 pm

My Ass have tried several methodes for P2P synthesis, and he decided, that method with PbOAc.3H20 is more convenient for him. But the main problem - the cleaning the flask from hard grey solids after reaction. It takes about 30-40 min, once he broke the one good flask.

He have found, that CaOAc also works and more convenient.... But it was not true. He recover back all PAA after 3 h heating of mixture of CaOAc and PAA. At the same time at the same temp. P2P using PbOAc was obtained with satisfactory yield.

So, Brain, what about Fe? Which yields, How did you clean the flask after use?

brain · Linguist Extraordinaire

the yeld was 62%, but ! the rest form flask, was treated h2so4 50%, and odbtained, some gray-yellowish mass, whih contain some paa, dryed and used again, to total yeld 67% of paa... [when the feoac i totaly dried, yeld is ~70%]-its maybe not huge-but for me its good enough Smile

-cleaning the flask is horror!! i hawe boughted 1 flask-only for this reaction! becauce gray-dark powder is "melting" with the glass-cant clean that.. Sad

... treated with HNO3+HCl [works~] but not in 100%...

Lief · Tue Mar 15, 2005 6:53 am

Try converting the PAA to the calcium salt using CaO or Ca(OH)2 (dissolved in water), CaCO3 doesn't seem to work. Adding some fused sodium acetate facilitates the reaction.

Recomended process: Using stoichiometry, calculate amount of CaO or Ca(OH)2 you need to react with PAA to get the calcium salt. Mix PAA and CaO or Ca(OH)2 together in water using a slight excess of CaO or Ca(OH)2. Stir until dissolved and reaction is complete. Add some acetic acid to convert the excess CaO or Ca(OH)2 to calcium acetate. Boil off the water and excess acetic acid and heat enough to dry the salts without too much decomposition. Mix with the required amount of calcium acetate and some fused sodium acetate and distill. If done right the distillate should smell sweet like pure P2P.