Are you still upset that the compound does not develop color and the product is difficult to determine? Today, the editor takes you into the magic world of color developers to present colors for your experiments.

Common color reagent and preparation method in chemical experiment

Are you still upset that the compound does not develop color and the product is difficult to determine? Today, the editor takes you into the magic world of color developers to present colors for your experiments.

In organic synthesis experiments, TLC plate is usually used to monitor the reaction, and the basic situation of the reaction system can be roughly seen by ultraviolet lamp irradiation, which is a simple and effective auxiliary means. However, ultraviolet lamps can only make some aromatic or conjugated compounds develop color, but cannot develop color for compounds without conjugated structure. At the same time, for some messy chemical reactions in the system, how to confirm the target product without the help of detection instruments has been perplexing all the scientific research partners.

Different chromogenic agents show different colors by combining with specific functional groups of the compound (e. g., double bond, hydroxyl group, aldehyde group, etc.). According to the color development, it can roughly determine whether the target product is generated, exclude other interference points, visually present the general situation of the reaction system, and provide convenience for subsequent separation and purification.

Today, Xiao Bian summarized the preparation methods of some commonly used chromogenic agents and shared them with everyone, hoping to bring some help to your scientific research partners.

1. Sulfuric acidGeneral purpose chromogenic agent

Common ratio: 1)5% concentrated sulfuric acid ethanol or acetic anhydride solution; 2) Concentrated sulfuric acid is mixed with methanol or ethanol in equal volume; 3)15% concentrated sulfuric acid n-butanol solution.

Methods: Spray or soak with any of the above test solutions, dry in the air for 15 minutes, and heat at 110 degrees Celsius to show color, or reach the highest fluorescence.

2. IodineGeneral purpose chromogenic agent

Common ratio: 1)0.5% iodine in chloroform.

Post-spray treatment: when the excess iodine on the thin layer is dispersed, spray 1% starch solution, and the spots turn blue. If there is excess iodine on the thin layer, the background will also turn blue.

2) iodine vapor: a little iodine crystal into a closed container, so that it is filled with saturated iodine vapor, the thin layer into the container for a moment or a few minutes that color. Sometimes put a small cup of water in the container to increase the humidity, can improve the sensitivity of the color, can improve the sensitivity of the color, in the compound spots yellow-brown.

3. Fluorescein-BromineDetection of unsaturated compounds

Common ratio: 100 mg fluorescein dissolved in 100 mL ethanol; Bromine reagent: 5% bromine in carbon tetrachloride solution.

Methods: After spraying fluorescein solution, the TLC plate was placed in the bromine reagent bottle, and the fluorescence could be detected under the ultraviolet lamp. Fluorescein combined with bromine was eosin color and no fluorescence. Unsaturated compounds will retain the original fluorescence after addition with bromine. If there are more spots, they will be yellow spots and the bottom plate will be red.

4. Silver nitrate-ammonium hydroxide: Detection of reducing compounds

Common ratio: 0.1 M silver nitrate solution and 5M ammonium hydroxide solution are mixed according to the ratio of 1:5, pay attention to the current use.

Method: After spraying, heat at 105 degrees Celsius for 5-10 minutes until dark black spots appear.

5. Bismuth potassium iodide reagentDetection of alkaloids and cesium salts

Common ratio: 0.85g bismuth subnitrate is dissolved in 10mL glacial acetic acid, and then diluted to 40mL with water; Liquid B 40% potassium iodide aqueous solution. In case of temporary use, take 5mL of liquid A and 5mL of liquid B, add 20mL of glacial acetic acid and 60mL of water, and shake well (brown reagent bottle can be used for a long time).

Methods: After the expansion of the thin-layer plate, dry directly after spraying bismuth potassium iodide reagent, orange red spots.

6. Phosphomolybdic acidFor reducing compounds, lipids, steroids, etc.

Commonly used ratio: 10g phosphomolybdic acid is dissolved in 100ml of ethanol, light yellow, and becomes light green for a long time, but it will not affect the use.

Methods: After spraying or soaking, heating at 120 degrees Celsius under the light yellow background is green spots, if the spots are too thick and dark yellow; The thin layer is fumigated with ammonia to fade the background color.

7、vanillin-sulfuric acidFor essential oils, higher alcohols, phenols, etc

Common ratio: vanillin 1g dissolved in 100ml sulfuric acid or vanillin 0.5g dissolved in 100ml sulfuric acid-ethanol (1:1) solution.

Method: After spraying or soaking the color developer, it is heated to the deepest color at 120 degrees Celsius.

8. Ferric chloride(ferric chloride) for phenolic, hydroxyamic acids.

Common ratio: 1%-5% ferric chloride 0.5mol/L hydrochloric acid solution.

Phenols are blue or green after spraying or soaking the developer, and hydroxyamic acid is red.

9. Alkaline potassium permanganate solutionCompounds containing reducing groups, such as hydroxyl, amino, aldehyde, etc.

Common ratio: 1.5g of potassium permanganate, 10g of potassium carbonate, 1.25mL of 10% sodium hydroxide aqueous solution, and 200mL of water are added to prepare a solution.

Methods: After the expansion of the thin layer board, dry directly spray alkaline potassium permanganate, heating dry, red background yellow spots.

10. Aluminum trichloride: for flavonoids.

Commonly used ratio: 1% aluminum trichloride ethanol solution, yellow fluorescence spots under long-wave ultraviolet light.

11. NinhydrinFor amino acids, amines and amino sugars

Common ratio: 0.2g ninhydrin is dissolved in 100ml of ethanol or 100ml of n-butanol, and 3ml of acetic acid is added.

Method: Spray or soak the developer and heat it at 110 degrees Celsius until the best color appears.

12. Aniline PhthalateFor reducing sugar.

Common ratio: 0.93g of aniline and 1.66g of phthalic acid are dissolved in 100ml of n-butanol saturated with water.

Methods: After spraying or soaking the developer, heating at 105 degrees Celsius for 10min, aldehyde hexose and methyl pentose were brown, aldehyde pentose was cherry red.

13. Ammonium molybdate-sodium sulfite:For sulfide, thiosulfate and phosphate

Common ratio: 1.5% ammonium molybdate 1M sulfuric acid solution; II.5% sodium sulfite solution.

Methods: After the thin plate is dried, solution I is sprayed first, solution II is sprayed, and heated at 105 degrees Celsius for 30min. Sulfide and thiosulfate are dark blue and phosphate is dark gray.

14, ammonium cerium nitrateFor the detection of alcohols

Common ratio: 1.1% cerium ammonium nitrate in 0.2M nitric acid solution; II. 1.5g of N,N-dimethyl-p-phenylenediamine hydrochloride was dissolved in a mixed solvent of methanol, water, and acetic acid (128ml +25ml +1.5ml), and equal weights of I and II were mixed before use.

Methods: After drying the sheet, spraying ammonium cerium nitrate chromogenic agent, heating at 105 degrees Celsius for 5min to show yellow spots.