Test kits: how do they work?

[mas49]

I was just curious if anybody happened to know how these work from an organic chemistry standpoint, or where I could find the info. Like what is the mechanism (arrow pushing, etc) for how they change the drug from an uncolored molecule to a colored one? Tried doing a Google search, but to no avail.

Haha sorry if this is too nerdy, but thanks!

 

[severely etarded]

The reagents are made of highly reactive chemicals that react when they come in contact with drugs. Different drugs produce different reaction. Some drugs produce no reaction at all, while some turn yellow ---> green, just plain yellow, some turn black slowly with smoke, some turn color very quickly. Some don't change color at all, bubble or fizz.

It's the same shit you see on the TV show "COPS" when they bust someone with drugs and do a field test to make sure. A baggie with powder in it could be cocaine, meth, or baking soda for all they know. They can determine the reaction by the color change

 

[mas49]

I know, but I'm talking about the actual chemistry behind it. Like how are the reagents transforming the chemical bonds of the drug molecules to make them into different colored compounds.

I'm a chemistry student, so I'm always curious as to how things like this work. :D

 

[severely etarded]

Like I said, the reagents are highly reactive chemicals Sulfuric acid is what the marquis is based from. I think the mandelin has sulfuric acid and sodium nitrate.

When they come in contact with various chemicals, a chemical reaction in an attempt to oxidize/neutralize the highly reactive substances with the chemicals being tested.

It's kind of like asking why does baking soda react with vinegar. One's an acid, ones a base, and they react.

Most drugs (but not all) react with the highly reactive reagents

 

[RavenousBlonde]

If you are a chemistry student, you might enjoy reading this:

http://www.eeel.nist.gov/oles/Publications/nij604-01.pdf

 

[adder]

Mandelin reagent has ammonium vanadate dissolved in conc. H2SO4. The link provided above shows how widely different reagents are used. They're not only in pill test kits. They're also used by some big shots when they buy a lot of cocaine/heroin/whatever. But they obviously got their chemists to prepare such reagents, this is not complicated. However, you often have to dissolve some substance in some solvent first to make such a test. It's all about the reaction that gives colorful products.

 

[phase_dancer]

I have drawn out the mechanisms for some of the reactions in the past. If I can find those I'll host them for you.


Ahh...here we are ( from Forensic Chemistry by Suzanne Bell and the Handbook of Chromatography)

1) Simons
2) Mandelin (basic oxidation of VO2+
3&4 Marquis

 

[mas49]

I have drawn out the mechanisms for some of the reactions in the past. If I can find those I'll host them for you.


Ahh...here we are ( from Forensic Chemistry by Suzanne Bell and the Handbook of Chromatography)

1) Simons
2) Mandelin (basic oxidation of VO2+
3&4 Marquis

AH! This is what I was looking for! Yeah, I was stumped on the Marquis reagent for a while. At 1st I thought you would make an iminium cation with the secondary amine and formaldehyde and then cyclize (via an electrophilic aromatic sub. rxn) which is assisted by the e- donating effects of the oxygens on the aryl group....then got stuck there (which was also fishy since you are in sulfuric acid which renders the nitrogen non-nucleophilic).

If you could host those other reactions then I would appreciate that a lot. Thanks for all of this. :D

 

[eon_blue]

Wow...that was nerdy

 

[mas49]

Wow...that was nerdy

That's how us chemistry people roll.

(Pun intended and not intended haha)

 

[RavenousBlonde]

Thanks for that info, p_d! We miss you around here!

 

[Bearlove]

Wow - good stuff indeed.

Ill just add this from the one and only 'Fast n Bulbous'

The formaldehyde forms coloured co-polymer type adducts, the sulphuric acid being there to catalyse the reaction (aldehyde + amine gives imines which then react with more formaldehyde). Also why they go off as all the formaldehyde is released from solution over time (analogous to soft drinks going flat over time as CO2 escapes, only much faster in carbonated drinks as CO2 is under pressure).

 

[phase_dancer]

The formaldehyde forms coloured co-polymer type adducts, the sulphuric acid being there to catalyse the reaction (aldehyde + amine gives imines which then react with more formaldehyde). Also why they go off as all the formaldehyde is released from solution over time (analogous to soft drinks going flat over time as CO2 escapes, only much faster in carbonated drinks as CO2 is under pressure).

I hate to have to comment here, but firstly, if you look at the above example of the reaction mechanism for Marquis with dimethylbenzylamine you'll see there is no imine produced (at least involved with the formation of the coloured product). Same goes for the reaction with opiates (see this link) Put simply, it is an acid catalyzed formation of a ring carbocation that results in the formation of the dimer which is coloured. mas49 has got it.

The above paper also contains other reaction examples.

Also, in over 3 years I spent researching reagents, several ~ 1L batches were stored in air tight schott bottles. Not once, even after several months, did I ever experience pressure release from opening a container, some of which were stored for over 9 months @ ~30 deg C. There may be some loss, but I'd argue it's pretty much insignificant. I think you'll find polymerisation of the formaldehyde accounts for at least some the discoloration. Formalin on it's on own polymerises when left on the shelf, producing a milky white solution. A few drops of added methanol fixes it.

 

[mas49]

I hate to have to comment here, but firstly, if you look at the above example of the reaction mechanism for Marquis with dimethylbenzylamine you'll see there is no imine produced (at least involved with the formation of the coloured product). Same goes for the reaction with opiates (see this link) Put simply, it is an acid catalyzed formation of a ring carbocation that results in the formation of the dimer which is coloured. mas49 has got it.

The above paper also contains other reaction examples.

Also, in over 3 years I spent researching reagents, several ~ 1L batches were stored in air tight schott bottles. Not once, even after several months, did I ever experience pressure release from opening a container, some of which were stored for over 9 months @ ~30 deg C. There may be some loss, but I'd argue it's pretty much insignificant. I think you'll find polymerisation of the formaldehyde accounts for at least some the discoloration. Formalin on it's on own polymerises when left on the shelf, producing a milky white solution. A few drops of added methanol fixes it.

Yeah an imine would never form in the presence of all of the sulfuric acid. It would be protonated, rendering it non-nucleophilic (and will never be able to form a bond to the formaldehyde).

At the last step of the marquis reagent, eventhough it wasn't shown, you somehow have to lose a hydride in order to form the benzylic carbocation. Where does this hydride go, and is the double aryl system provide enough stability for that to happen?

EDIT: I guess it would more than likely react with one of the molecules of H2SO4 to form hydrogen gas?

 

[phase_dancer]

I'd suggest that after the diphenylbenzyl is formed, oxidation would occur, catalysed by iron traces in the sulphuric, and the acid itself, which would result in formation of the sec. alcohol, although I'm unsure of the mechanism. As it is known that carbocations can be generated by protonation of the lone pair of electrons if the protonated atom is a better leaving group [Sykes] the last step would likely involve protonation followed by dehydration, which would form the carbenium ion. Due to inductive effects/ resonance stabilisation, the benzhydryl cation would be quite stable.