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	Posts 1 - 14 of 14	Subject: Rxn parameters of HI/P reduction affecting purity



Rhodium (Chief Bee) 07-28-01 19:07 No 199559	Rxn parameters of HI/P reduction affecting purity	Bookmark Reply
	LITHIUM-AMMONIA AND HYDRIODIC ACID/RED PHOSPHORUS REDUCTIONS IN CLANDESTINE LABORATORIES G. S. Kamali Kannangara, Ian Rowney, Philip Maynard and Michael Dawson Department of Chemistry, Materials and Forensic Science, University of Technology Sydney, P.O. Box 123, Broadway NSW 2007, Australia In this study, the effect of light and temperature on the reduction of N,N-dimethyl-3-phenyl-3-hydroxypropylamine (DPHPA) via hydriodic acid /red phosphorus (HI/P) were examined with a view to acquire a better understanding of the mechanism of the reaction and to explain the occurrence of possible by-product(s). Another reduction procedure that was discovered recently upon seizure of a clandestine methamphatemine laboratory in Vacaville, California, USA, involved the use of lithium-ammonia and ammonium chloride. Therefore, the effect of temperature, presence of water and relative molar ratios of the reactants for this modified Birch reduction of DPHPA was investigated. The progress of all the reactions were monitored by gas chromatography-mass spectrometry (GC-MS) and nuclear magnetic resonance spectroscopy (NMR). The results of the HI/P reaction show that the formation of the alkene intermediate occurs very rapidly. It is important to note that all of the DPHPA is converted almost instantaneously to the alkene, the major reaction intermediate. Further studies revealed that the yield and purity of alkane product improved at higher temperatures (120°C). It was also found that when the reaction was carried out in the dark, the rate of the reaction decreased significantly which is most likely due to the role light plays in the equilibrium of the dissociation of hydriodic acid. It is of interest to note that fewer impurities were formed in the dark reaction that gives an indication of the other roles light could play in alternative reaction pathways. The use of the modified Birch reduction on DPHPA afforded the reduced product with high purity. The major difference between the two reduction procedures is the rate of conversion of DPHPA to the alkane product. The HI/P takes at least 3 hours for the reduction whereas the Birch reduction is almost complete after 10-20 mins. A comparison of the impurity profiling using GC-MS and NMR spectroscopic methods was established. These results give more useful information on the reduction of DPHPA that will enable the law enforcing agencies to have a better understanding of the clandestine reduction of pseudo ephedrine to produce amphatemines.



terbium (Hive Addict) 07-29-01 05:36 No 199670	Re: Rxn parameters of HI/P reduction affecting purity	Bookmark Reply
	The results of the HI/P reaction show that the formation of the alkene intermediate occurs very rapidly. It is important to note that all of the DPHPA is converted almost instantaneously to the alkene, the major reaction intermediate. So, dehydration of ephedrine to the alkene is part of the reaction pathway? What happens next? Can anyone enlighten me?



Rhodium (Chief Bee) 07-29-01 05:57 No 199676	Re: Rxn parameters of HI/P reduction affecting purity	Bookmark Reply
	HI readily adds across the bond (formation of iodoephedrine), HI dissociates (due to heat, light, or even H2O2 some cooks add) forming an I radical, this radical associates with the I on the iodoephedrine, I2 dissociates from the rest of the molecule, leaving it with a relatively stale benzyl radical, which attracts a hydrogen (from for example HI) forming yet another I radical in this radical-process (which termimates when the I binds to either H radicals or other I radicals). http://anon.user.anonymizer.com/http://www.rhodium.ws



b159510 (Professional Student) 07-29-01 06:47 No 199685	Re: Rxn parameters of HI/P reduction affecting purity	Bookmark Reply
	Compare your result to the one I reached, they could be twins..Though I like mine better..b159510: "Re: RP/I reaction" (Chemistry Discourse) Back to the Primitive



b159510 (Professional Student) 07-29-01 07:06 No 199694	Re: Rxn parameters of HI/P reduction affecting purity	Bookmark Reply
	HI readily adds across the bond (formation of iodoephedrine Given that some water is always(I think) added at the start of the reaction, and the reaction environment is acidic, wouldn't it be more likely that ephedrine is reduced via the S_N1 pathway rather than the elimination pathway that would form the double bond? (also considering the stability of the benzylic carbocation) Back to the Primitive



Rhodium (Chief Bee) 07-29-01 15:34 No 199748	Re: Rxn parameters of HI/P reduction affecting purity	Bookmark Reply
	Most likely there is a variety of competing mechanisms, depending on the reaction procedure. There are almost as many methods as there are cooks, and this will probably influence the exact mechanism in a variety of ways. But if the researchers above did indicate that the alkene was the main intermediate in their reaction, their reaction parameters fits well with the mechanism I described (creds to b159510 for his ideas). The aziridine is one of the major by-products of HI/P reduction. At what stage does it form, and by what mechanism? Is it just a simple SN2 of iodoephedrine? http://anon.user.anonymizer.com/http://www.rhodium.ws



b159510 (Professional Student) 07-30-01 12:46 No 199989	Re: Rxn parameters of HI/P reduction affecting purity	Bookmark Reply
	So what is this DPHPA molecule anyway? Methylephedrine using some backward numbering system? Back to the Primitive



Rhodium (Chief Bee) 07-30-01 15:20 No 200011	Re: Rxn parameters of HI/P reduction affecting purity	Bookmark Reply
	b159510: It is either methylephedrine, or the n-propylamine analog. http://anon.user.anonymizer.com/http://www.rhodium.ws



jim (Hive Bee) 07-30-01 21:17 No 200071	Re: Rxn parameters of HI/P reduction affecting purity	Bookmark Reply
	From what I remember the aziridine impurity is formed from the amine protonation, and the aziridine then decomposes into P2P, via ephedrine's abnormal hydramine fission. This means that the aziridine is formed before alkENE formation. I beleive that this is in Forensic Science International 39, 39-53 (1988). A nice diagram accompanies it I beleive. I don't know what conditions favor the aziridine formation, but I think that the very same conditions listed under the hydramine fission of ephedrine to form P2P will give you a good idea. This paper leans more credance to the addition of Al to the reaction. Adding Al creates Al2O3, which absorbs water, and promots dehydration of ephedrine. The Al2O3 also buffers the solution thus reduces the likely-hood of protonating the amine. What do you think?



b159510 (Professional Student) 08-03-01 14:30 No 200994	Re: Rxn parameters of HI/P reduction affecting purity	Bookmark Reply
	I wish we had access to the entire paper, not just the abstract. I assume this DPHPA is actually methylephedrine. Damn pig chemists and their little games. I imagine the reaction here is generating the HI in situ, because I don't see how the alkene would form before the iodide if hydriodic acid was used. There might be enough non-protonated water left so it could go around ripping the hydrogen of the #2 carbons. I guess it could happen. I really haven't looked into how fast the dry RP/I can form phosphoric acid, but it seems reasonable to think the alkene is formed here. The iodine radical bonds with the less substituted carbon, so thats all good. Plus it only needs a small amount of the phosphoric acid. Still, it seems a little strange. The iodine isn't exactly in love with the carbon, so the addition step would be slow. Oh well, enough rambling for one day. Back to the Primitive



Stonium (Moderator) 08-04-01 19:14 No 201340	Re: Rxn parameters of HI/P reduction affecting purity	Bookmark Reply
	I wish we had access to the entire paper, not just the abstract. Maybe you said so and I missed it, but has someone checked and found it to be unavailable? If not, I can check for it at the wonderful university medical school library (with an emphasis on forensics ) which is nearby my hacienda. Ok, ok, you smooth talker, you. Talked me into it...I'll check it out today. Welcome, Stonium _{Philosophy: unintelligible answers to insoluble problems.}



b159510 (Professional Student) 08-04-01 20:10 No 201348	Re: Rxn parameters of HI/P reduction affecting purity	Bookmark Reply
	, but has someone checked and found it to be unavailable I really don't know where to look. I don't have access to the pig journal at school or online. I checked out the university website in Australia, and the site where the abstract is posted, but I couldn't find more info. Back to the Primitive



Stonium (Moderator) 08-05-01 10:11 No 201486	Re: Rxn parameters of HI/P reduction affecting purity	Bookmark Reply
	The pig journal? Huh? I musta missed that somehow. Hmmm..well I guess my library won't have it then... Tarred, Stoni _{Philosophy: unintelligible answers to insoluble problems.}



b159510 (Professional Student) 08-06-01 00:48 No 201630	Re: Rxn parameters of HI/P reduction affecting purity	Bookmark Reply
	The aziridine is one of the major by-products of HI/P reduction. At what stage does it form, and by what mechanism? Is it just a simple SN2 of iodoephedrine? Assume that there would be protonated and nonprotonated amine in equilibrium. The position shifted toward protonation. The lone pair of the nonprotonated nitrogen could displace the iodine via the S_N2 pathway. The paper on Rhodiums site says 1,2-dimethyl, but I only see the one methylated carbon and the N-methylaziridine. This corresponds with the MW of 147 they give. I don't really get their nomenclature, but I would guess they are the same molecule. This aziridine seems like it would be unstable and not likely to survive a post reaction workup.[EDIT] Actually that would not be an SN2 mechanism. Maybe internal SN2, or SN intramolecular. Back to the Primitive

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