Introduction To The Simon's Reagent

Simon's reagent is a mixture of sodium nitroprusside, sodium carbonate and acetaldehyde. This reagent is selective towards secondary amines. A characteristic blue coloration appears when the test is positive.

Testing with the Simon's reagent will give a different information on the drug structure than the Mecke, Mandelin and Marquis reagents. As the latter will distinguish compounds between their substituents on an aromatic cycle, Simon's reagent will assess of the presence of a reactive amine function on the drug tested. Therefore cross testing a compound with Simon's reagent, Robadope variant (see the section on robadoe for more info) and one of the three reagents among Mecke, Mandelin and Marquis usually allows for the identification of the drug(s) present in a compound (or at least the classes of drug present).

Testing with Simon's Reagent

The procedure is as follows: Add 1 volume of solution A to the drug, followed by 2 volumes of solution B (see the "Making Simon's reagent" section for details on how those solutions are made). Notice the change in color and the rate of change.

The nitroprusside complex is red and so are its solutions. Thus, a red coloration of the tested sample can not be interpreted as a positive result, nor it is related to the fact that some reaction occured.

Making Simon's reagent

Solution A: Dissolve 1 g of sodium nitroprusside in 50 mL of distilled water and add 2 mL of acetaldehyde to the solution with thorough mixing.
Solution B: 2 % sodium carbonate in distilled water.[1]

Procedure: Add 1 volume of solution A to the drug, followed by 2 volumes of solution B.[1]

Safety considerations

Sodium nitroprusside:
- WARNING: Contact with acid liberates cyanide gas.
- May cause respiratory tract irritation. May cause eye or skin irritation. Harmful if inhaled, swallowed or absorbed throught the skin.
- Wash toroughly after handling. Use only in a well-ventilated area. Do not get on skin or in eyes. Do not ingest or inhale. Avoid breathing dust, vapor, mist or gas.

Acetaldehyde:
- May cause eye or skin irritation. Harmful if inhaled, swallowed or absorbed throught the skin.

Sodium carbonate:
- May cause respiratory tract irritation. May cause eye or skin irritation. Harmful if inhaled or swallowed.

Due to the potential hazards associated with improper handling of sodium nitroprusside, it is recommended to buy pre-made commercial testing kits, or at least pre-made sodium nitroprusside solutions.

How the Simon's Reagent Works

Reaction with Simon's reagent yields a definite blue-colored compound. Unlike Marquis, Mandelin and Mecke reagents, the Simon's reaction involves the amine functional group of the drug compound.

General mechanism

The reaction proceeds by condensation of the amine (1) and acetaldehyde yielding the imine (2) then the enamine (3) after deprotonation. The enamine adds on the nitroso ligand of iron. It has been shown that the nitroso ligand in the nitroprusside complex is NO⁺, therefore the iron in the complex is in the 2+ state. Upon addition of the enamine, an iminium salt (4) is produced. This salt is subsequently hydrolysed, releasing the starting amine (1) along with a complex named the Simon-Awe complex (5).



This last compound is blue-colored and accounts for the coloration resulting for the test. It can also be noted that two mesomeric forms can be used to describe this complex (as depicted in the corresponding box).

From the mechanism it is clear that only amines can react with Simon's reagent. Moreover, tertiary (and quaternary) amines are not reactive, as they are unable to form the enamine. Sodium nitroprusside only reacts with secondary amines in the presence of acetaldehyde, and only with primary amines in the presence of acetone[2]. However, it is not possible to determine from the mechanism given why Simon's reagent is selective toward secondary amines, and why the robadope variant is selective toward primary amines. It is possible that the formation of the intermediate (4) is more complex than depicted and may involve many steps.

Additional notes

Considering that two products react with Simon's reagent, the difference between them will result for the kinetics of the reaction, the rate at which the Simon-Awe complex is produced. Hence, when performing a Simon's reagent test, it is important to check the rate of coloration, as this provides additional information on the nature of the compound.

Factors influencing the rate of formation include:
- The rate of formation on the enamine (3). For example, an amine having large substituents may condense slower than an amine having small substituents, thus resulting in a faster coloration for the latter.
- The addition rate of the enamine (3) on the nitroprusside complex. The more active is the enamine, the faster the addition takes place. This may be the reason for the slower reaction taking place with methylone than with MDMA, the carbonyl group may inactivate the enamine.

Different references[2][3] describe the Simon-Awe complex as being either charged 3 - or 4 -. The difference lies in the presence or absence of a proton, which can be seen bonded to the oxygen on the lower right complex.

Testing with Simon's reagent (or robadope) could theoretically reveal positive from the reaction with an amine which is an inactive adulterant or an excipient. This would lead to a misinterpretation of the result, attributing the positive result to the presence of a drug instead of an inactive compound. However, this is very unlikely to happen as amines are usually pharmacologically active. Thus a positive testing with Simon's reagent can reasonably be associated to the presence of an active compound in the tested sample.

Known positive reactions with Simon's Reagent

Compound	Color	Reaction rate
ephedrine	bluish dark [1]	no data
MBDB	bluish dark [1]	no data
MDAI	no reaction [1]	-
Methylone	no reaction [1]	-
Ethylone	no reaction [1]	-
Butylone	no reaction [1]	-
4-methylamphetamine	no reaction [1]	-
4-fluoroamphetamine	no reaction [1]	-
d-methamphetamine	dark blue [2]	no data
dimethoxymethamphetamine	deep blue [2]	no data
methylphenidate	pale violet [2][3]	no data

Robadope variant

Robadope is similar to Simon's reagent, replacing acetaldehyde with acetone. This variant is selective toward primary amines. A positive test result is characterized by a purple color. The colored complex responsible for the coloration is depicted below. Note the methyl group next to the carbonyl.

Known positive reactions with Robadope

Compound	Color	Reaction rate

Comparision of Simon's and Robadope reagents

Selectivity of the reagents

Simon's and robadope testing can be combined to determine wheter primary or secondary amines are present in a pill.
Amines exist as four types :
- Primary amines, possessing only one alkyl substituent (example: MDA, 2-CB)
- Secondary amines, possessing two alkyl substituents (example: MDMA, methamphetamine)
- Tertiary amines, possessing three alkyl substituents (example: DMT, MDPV)
- Quaternary ammonium salts, possessing four alkyl subsituents and which are positively charged (example: tetramethylammonium)



The mechanism of the reaction with robadope or Simon's reagent involves the formation of an enamine, via the formation of an imminium salt resulting from the condensation of the amine with the carbonyl compound.
The imminium salt can not form when the amine is tertiary or quaternary. Indeed, the first step involves a nucleophillic addition of the amine on the carbonyl. This is impossible for quaternary amines as they do not have a non-bonding electron pair. The second step is an elimination of a water molecule involving an other electron pair on the nitrogen, resulting in the formation of the imminium salt. This step is impossible for tertiary amines.
Therefore, Robadope and Simon's reagents won't test for tertiary amines (nor quaternary ammonium salts, althought no drugs are quaternary ammonium salts) like DMT, LSD, LSA, DiPT, MDPV, etc.



Both reagents can a priori react with secondary and primary amines. However, Simon's reagent is only selective towards secondary amines and robadope only toward primary amines. Yet, the reason why robadope and Simon's exhibit different selectivity is not clear.

Application

Consider that a pill sold as ecstasy contains a mixture of MDMA, MDA and methamphetamine. MDMA and methamphetamine are secondary amines, MDA is a primary amine. A test with Simon's reagent will show positive due to reaction of both methamphetamine and MDMA. A test with Robadope will also give a positive result. At this point it is sure that the pill contains at least two different compounds (both primary and secondary amines) which are likely to be active.



However, it is impossible to know how much different primary and secondary amines are present. In this case there are two secondary amines, MDMA and methamphetamine, which are not distinguished by Simon's reagent, and one primary amine, MDA. A complementary test with another reagent, for example Marquis reagent, could assess of the presence of a non-substitued amphetamine.

Compound	amine class	Simon's result	Robadope result	Marquis result
MDMA	Secondary	Positive	Negative	blue-purple-black
MDA	Primary	Negative	Positive	blue-purple-black
Methamphetamine	Secondary	Positive	Negative	orange-red

Compounds tested with Simon's and Robadope reagents

Compound	Verified?	Color	Other notes

References

1. ^ a bReagent A.12. Colour Test Reagents-Kits for Preliminary Identification of Drugs of Abuse. National Institute of Justice.
2. ^ a bIonic Equilibria in Analytical Chemistry, J-L. Burgot, Springer, 2012
3. ^Chemistry and Reaction Mechanisms of Rapid Tests https://drugs-forum.com/forum/loc...id=17&id=12434