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The Marquis reagent is one of many drug identification reagents. It changes color in the presence of a compound in a predictable fashion and can be used to help infer the potential identity of a compound.


[top]Introduction To The Marquis Reagent

The Marquis reagent is used to identify aromatic compounds. The coloration is due to a compound formed by condensation of multiple drug molecules. The obtained color is therefore related to the nature of the tested drug. The coloration is distinct between classes of drugs, for example between opiates and amphetamines. However, the reagent fails to unambiguously distinguish between two drugs in the same class, as the colorations may differ only by a slight shade. Therefore, multiple tests are sometimes required to efficiently identify a compound.

Its advantage is that it can test for phenethylamines like 2C-x and DXM. Tests for: MDxx, (meth)amphetamine, 2C-x, DOx, DXM. It will also react with aspirin, some opiates, LSD, mescaline, methylphenidate and sugar.

[top]Testing with Marquis Reagent

One can apply a few drops of the Marquis reagent to a sample of the compound on glass or ceramic. Be careful with test regents, they can be corrosive. Handle in a well ventilated area, gasses can emerge from the reaction.

Observe the color change. Compare with chart below. [1]

[top]Known Color Changes with Marquis Reagent

Aspirin powder Deep red
Benzphetamine HCl Deep reddish brown
Chlorpromazine HCl Deep purplish red
Codeine Very dark purple
d-Amphetamine HCl to Strong reddish orange to Dark reddish brown
d-Methamphetamine HCl Deep reddish orange to Dark reddish brown
Diacetylmorphine HCl Deep purplish red
Dimethoxy-meth HCl Moderate olive
Doxepin HCl Blackish red
Dristan powder Dark grayish red
Exedrine powder Dark red
LSD Olive black
MDA HCl Black
Meperidine HCl Deep brown
Mescaline HCl Strong orange
Methadone Light yellowish pink
Methylphenidate Moderate orange yellow
Morphine monohydrate Very deep reddish purple
Opium Powder Dark grayish reddish Brown
Oxycodone HCl Pale violet
Propoxyphene HCl Blackish purple
Sugar crystals Dark brown

[top]Making Marquis reagent

Carefully add 100 mL of concentrated sulfuric acid to 5 mL of 40 percent
formaldehyde (v:v, formaldehyde:water).[2]

[top]Danger of the Marquis Reagent

1. Formaldehyde - TOXIC. May cause cancer. May cause heritable genetic damage. Toxic by inhalation, in contact with skin, and if swallowed. Causes burns. May cause sensitization by inhalation and skin contact. Readily absorbed through skin.L achrymator.Combustible. Target organs: eyes, kidneys. Wear suitable protective clothing and gloves.[2]

2. Sulfuric acid - OXIDIZER, ACID, TOXIC, CORROSIVE. Liquid and mist
cause severe burns to all body tissue. May be fatal if swallowed. Harmful if inhaled.
Inhalation may case lung damage. Do not get liquid in eyes, on skin, or clothing. Wash thoroughly after handling. Avoid breathing vapors. Use with adequate ventilation. Do not add water to contents while in container because of violent reaction. Store in tightly closed container. Wear suitable protective clothing and gloves.[2]

[top]How the Marquis Reagent Works

The Marquis reaction proceed by the condensation of drug molecules, yielding carbocations or larger unsaturated compounds which are colored. The reaction is selective toward activated aromatic cycles.

[top]General mechanism

The drug molecule (1) undergo an electrophylic substitution by the protonated formaldehyde (2). The carbocation (3) obtained reacts with another drug molecule yielding a dimer (4). The dimer is subsequently oxidized (concentrated sulfuric acid behaves as an oxidizer) to give a stabilized carbocation (5). This last compound is colored and is responsible for the color observed.

The regioselectivity of the addition of formaldehyde is determined by the usual selectivity rules for electrophilic substitutions.


The previous mechanism must be refined for each compound. Below are given two examples for which the mechanisms have been elucidated.


The reaction in the case of morphine differs sligthly from the previous scheme since two formaldehyde molecules (in red) are involved in the condensation, thus forming a cycle. Subsequent oxidization of the cycle leads to the formation of the purple/violet carbocation.[3]


The case of methamphetamine fits perfectly with the general mechanism given above. The colored compound and produces an orangish color[3].There is also a possibility of condensation in the ortho position. However, the latter is much more strained and thus the amount produced is far less inferior to that of the depicted carbocation, leading to less polymerization and thus a clearer color.

[top]Additional notes

The previous examples given show an unambiguous colored product. However, this is not always the case. For many molecules, there are multiple potential condensation sites, therefore leading to multiple colored compounds. Polymerization can also occur if the aromatic cycles are sufficiently reactive (for example with MDMA).

In such cases, the compound tested will give a dark brown or black coloration, resulting from the multiple different absorption wavelengths. This situation is the same as when mixing many paints of different colors: the resulting mixture is dark brown.

The color obtained depends on the composition of the starting reagent. Pre-made kits availabe over the internet are prepared the same way and thus the results from these tests are reproductible. However, hand made reagents will have some small variations in their composition, leading to slightly different results (shades of color will vary). For example a reagent containing more formaldehyde will induce more polymerization thus a darker coloration.

The presence of adulterants in the tested product may also affect the resulting coloration:
- Firstly, the adulterants may react by themselves with the reagent adding their own coloration to the result.
For example if some sugars are present (lactose for example), they will caramellize in the presence of sulfuric acid, thus producing a brown coloration. This is not the result of a marquis reaction, but only the reaction of the sugar with sulfuric acid.
Another case is if some aromatic compounds are present (like acetaminophen), they will undergo a marquis reaction, therefore yielding their own coloration which will superpose to give the resulting coloration.
- Secondly, the adulterants may react with the drug forming cross condensed products yielding a different color.

[top]Compounds tested with Marquis Reagent

The following is a list of compounds tested by Drugs Forum members with the Marquis reagent.

Verified refers to whether or not the compound was verified by a third party lab (ie. GC/MS results confirm).

Color refers to the best description of the color either by image upload or user(s) description. Please see the thread linked for more information.

Compound Verified? Color Other notes
2C-T-7 [1] no light orange progressing to orange  
25B-NBOMe [1] no first yellow then going to light green  
25C-NBOMe [1] no start's orange going to golden and then to green  
25I-NBOMe [1] no dark green crystalline and white
25I-NBOMe [2] no dark green/brown very white but more dusty
25I-NBOMe [3] no dark green yellowish and lumpy
25I-NBOMe [4] no dark green/brown white dusty and maybe freebase
4-FA [1] no Bright Yellow  
4-FA [2] no Bright Yellow  
4-FA [3] no Light Orange user believes this is 4-FA
4-FMA [1] no Yellow/ dark yellow. Spot of pink. user comments this compound is barely active in high doses
5-APB [1] no between brown red and violet  
6-APB [1] no Dark Brown user describes this compound as supposedly 6-APB, though very impure
6-APB [2] no Purple Reacts as should with EZ test MCPP test which also tests for 6-APB
DOC [1] no fizzing and bubles, then green  
DOC [2] no Deep Green consistent with results from other users
DOC [3] no Deep Green consistent with results from other users
DPT no Yellow, Olive  
JWH-073 [1] no dark brown  
JWH-081 [1] no orange > orange/green/brown  
JWH-250 [1] no red/orange  
MDPV [1] no Orange no rxn to Simons or Robadope, implies tertiary amine (MDPV)
MDPV [2] no Orange no rxn to Simons or Robadope, implies tertiary amine (MDPV)
Methylone [1] no Yellow consistent with EZ Test results
Methylone [2] no Orange consistant with EZ test result
Butylone [1] no Orange consistant with EZ test results
Mephedrone [1] no pale yellow pure Mephedrone supposedly show no reaction
Mephedrone [2] no pale yellow pure Mephedrone supposedly shows no reaction
Naphyrone [1] no Bright Orange rxn to Simons, implies secondary amine (not Naphyrone)
Benzo-Fury Pellet [1] no Purple


  1. ^ EZ Test Marquis: The classic test for ecstasy. EZ Test. Located here: http://www.eztest.com/dir2/ez-test-marquis-the-classic-test-for-ecstasy. (Accessed July 29, 2011).
  2. ^ a b c d Reagent A.5. Colour Test Reagents-Kits for Preliminary Identification of Drugs of Abuse. National Institute of Justice.
  3. ^ a b Chemistry and Reaction Mechanisms of Rapid Tests https://www.drugs-forum.com/forum/loc...id=17&id=12434

Created by NeuroChi, 29-06-2011 at 17:38
Last edited by John_bob, 18-10-2014 at 13:56
Last comment by John_bob on 18-10-2014 at 14:01
8 Comments, 48,845 Views

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