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Author: Subject: Ammoniolysis of phthalate esters
Boffis
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[*] posted on 8-4-2013 at 18:12
Ammoniolysis of phthalate esters


I recently acquired 500ml each of di(n-butyl) and di(n-pentyl) phthalates, they are not much use to me but since they cost nothing they were gladly received. Phthalamide, however, is more interesting and so I decided to try and convert them to phthalamide but simply reacting them with 0.90 SG ammonia (>25%) solution.

Experiment:
50ml of n-pentyl phthalate was placed in a heavy glass "Schott" type wide mouth reagent bottle with 50ml of the ammonia solution. The lid was screwed on securely and then the bottle shaken until a white emulsion formed. After about an hour it had seperated again so I added 50ml of isopropanol in the hope it would improve miscibility and shuck the bottle again. I have been shaking the bottle several times a day for about a week and I now have to leave if for a month or so because of my work. So far no visible reaction has occurred. It was store in the light at about 23-24 C.

Has anyone else tried this reaction? Any details, ideas or some idea as to how long this reaction might require, does it require elevated temperatures?

I have search the Board for posts on this or related subjects and the only one I could find referred to the ammoniolysis of PET from bottles, requiring 3wks at room temperature in the light. Was the ipa a good idea or will it just dilute the ammonia? Do anyone think a phase transfer catalysis would be a help (it would still need shaking).
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Adas
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[*] posted on 9-4-2013 at 07:04


Don't mess with phthalates without proper ventilation! They can cause infertility among other health problems.

Better method, IMO, would be to hydrolyze them with NaOH, you would get the Na phthalate and aliphatic alcohols. Then react the Na phthalate with NH4Cl.




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Nicodem
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[*] posted on 9-4-2013 at 08:47


Direct ammonolysis of dialkyl phthalates to phthalimides can be low yielding and practical only for dimethyl phthalates. For example, substituted dimethyl phthalates gave low to moderate yields of the corresponding phthalimides after treatment with gaseous ammonia in ethylene glycol at 120 °C (DOI: 10.1021/jm00033a019 and 10.1021/jo051096o). I can only imagine that the yield for the dipentyl ester would be terrible.
The most effective method is the indirect ammonolysis with urea in refluxing alcohols using sodium alkoxides as the bases (Ber. 46, 1913, 2560–2564, attached). Unlike the direct ammonolysis, this reaction should not be hindered by the longer chain alkyl phthalates and should work on your dipentyl ester (transesterifications occur rapidly under such reaction conditions). Anhydrous ethanolic sodium ethoxide is very simple to prepare from NaOH as described elsewhere on this forum.
Quote: Originally posted by Adas  
Don't mess with phthalates without proper ventilation! They can cause infertility among other health problems.

Check the literature before posting misinformation!
Quote:
Better method, IMO, would be to hydrolyze them with NaOH, you would get the Na phthalate and aliphatic alcohols. Then react the Na phthalate with NH4Cl.

Please give us the reference.

Attachment: cber.19130460318.pdf (232kB)
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Boffis
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[*] posted on 9-4-2013 at 08:59


Thank you for your concern Adas but I have a well equipped laboratory and I work on the asumption that if its in my laboratory its toxic or overwise hazardous.

Secondly the vapour pressure of these higher alkyl phthalate is extremely low at room temperature and I don't go around eating them.

Thirdly the toxicity of phthalate is such that it requires prolonged exposure and any one more thatn 30 years of age has already been exposed to a whole range of phthalates which were once used in just about every houshold product as fatty oil substitutes since they don't putrify, as plastisers, in cosmetics and medical creams etc. The two bottle I acquired came from a vetenary practice where these compounds were permitted for external use until very recently, hence the reason they have become available.

Moving on to technical issues, the hydrolysis of butyl phthalate with sodium hydroxide involves high temperatures (near boil NaOH solution I've already tried this) and hence higher vapour pressure.

I have, however, discovered a short note on the ACS web site via a google search from the J Chem Ed. that, because its only one page, can be viewed for free. In this note it discusses ammoniolysis of esters and the ease with which it occurs. Basically lower molecular weight hydrolyse rapid and yield amides in high yield. So methyl and ethyl formates and acetates give amides rapidly in 73-87% yields the propyl and butyl ester more slowly and in lower yields. It then goes on to say that for high esters it is better to use transesterification to get the methyl ester and then ammoniolyse the product. This is basically and extension of the biodiesel process using sodium methoxide and methanol to convert the the higher ester to a methanol ester and then ammoniolyse that.

I'll try this when I next have time and report back. There must be gallons of old phthalate ester lying around.

Thank you for the reference Nicodem, I'll try this when I get time. Anhydrous sodium alkoxide is not a problem.


[Edited on 9-4-2013 by Boffis]
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Adas
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[*] posted on 9-4-2013 at 10:29


Quote: Originally posted by Nicodem  

Check the literature before posting misinformation!


This is not misinformation, I have read it elsewhere... O.o Maybe you saw different literature, but still, one has to be careful with this stuff.




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[*] posted on 10-9-2013 at 14:07


Well, since the direct ammoniolysis of di-n-pentyl phthalate didn't work in the slightest as Nicodem suggested, I decided to try transesterification to the methyl ester instead. I used the 50ml of ester from the first experiment which I first washed free of ammonia with water and then used it without further purification. I dissolved 0.23g of KOH (4 pellets) in 60ml of laboratory grade methanol, warming was required, and then mixed it with the phthalate ester in a 250ml round bottom flask, refluxed for 10 minutes and cooled. The mixture did not separate as it does with biodiesel so I put it in a separating funnel and added water drop-wise; it quickly became cloudy and quite suddenly began to separate into two layer. I separated the lower layer which smelt rather peculiar and was presumably the pentanol-methanol-water-KOH mixture. The upper layer was shaken with water (in which it now sinks) and then separated and dried with CaCl2, filter to remove an insoluble scum and then distilled up to 200 C (the upper limit of my thermometer). Dimethyl phthalate boils at 283-285 C so the residue in the flask is most phthalate esters (about 30ml) but I have no means of testing its purity. The smaller amount of distillate came off mostly between 100 and 130 C so is probably methanol and pentanol.

The original aqueous layer was found to separate again if more water was added. I separated it and dried it with CaCl2 and got a horrid gunky mess that slowly separated over a few days into a dense saturated CaCl2 solution and a cloudy organic layer and a little solid. I separated the aqueous phase and vacuum filtered the residue which slowly separated into two layer. The lower layer is cloudy but the upper layer is clear. I tested the upper layer by oxidising it with dichromate and dilute sulphuric acid and got the unmistakably rancid small of n-pentanoic acid. I haven't had time to test the lower layer but I presume that it is more phthalate.

It appears that I should have added more water to start with since the excess methanol appears to cause the pentanol to partition between the two phases. Less methanol may also help ease the separation. A fair amount of pentanol is present in the original organic phase because it floats were dimethyl phthalate is significantly heavier than water (D=1.18)

It therefore appears that the phthalate esters transesterify fairly readily. When I am next at home I will complete the work up and report the yields of product (I just purchased a high temperature thermometer off ebay). I will then attempt to convert it to phthalimide.
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