Methyl Red CAS 493-52-7

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  • Appearance: Reddish-violet solid
  • Purity: 99. 0%min
  • Stock: In stock
  • Sample: Available
  • Zhishang Chemical: Methyl Red Supplier & Manufacturer

Basic Info

What is Methyl Red?

The molecular formula of methyl red is C15H15N3O2. Molecular weight 269.31. Luminescent purple crystals were obtained from toluene. Melting point 183°C, pKa1=2.5, pKa2=9.5, pKb=4.8. Soluble in ethanol, acetone, benzene, chloroform, acetic acid, almost insoluble in water. Preparation method: derived from the coupling of the diazotization product of anthranilic acid and dimethylaniline. Uses: When mixed with 0.1% ethanol solution, it can be used as an acid-base indicator. It is red at pH 4.4 and yellow at pH 6.2. Widely used in strong acid and weak base titration, because it is easy to be oxidized and faded, so the reading must be read immediately when the titration end point is reached.

The existing methods for synthesizing methyl red use ethanol as the reaction medium in some places, the cost is high, the product is difficult to filter, and the yield is low. Some adopt water as the reaction medium, although the yield (66%) is improved, but still There are the following problems: the amount of acid and base is large, and when anthranilic acid is diazotized, hydrochloric acid equivalent to more than twice the molar amount of anthranilic acid is added, so that a large amount of alkali needs to be added to neutralize the excess acid in the coupling reaction step. In the coupling reaction, the amount and speed of addition of alkali directly affect the yield and quality. It is necessary to control the amount and speed of addition of alkali, so the operation is complicated. The generated methyl red is an amorphous precipitate, which is thick and difficult to filter and difficult to wash. , The purity of the crude product is not high, and it is generally purified by recrystallization from an organic solvent.

Methyl Red Uses

  1. Methyl red is one of the commonly used acid-base indicators, its normal concentration is 0.1% ethanol solution, pH4.4 (red)-6.2 (yellow). Also used for protozoan vital staining.
  2. It can titrate ammonia, weak natural bases as well as alkaloids, yet except natural acids apart from oxalic acid and picric acid; it can be combined with bromocresol environment-friendly and also methylene blue to form a combined indication to reduce the shade variety as well as improve the sensitivity of color adjustment.
  3. Methyl red can be made use of as an adsorption sign for precipitation titration, such as titrating fluoride ions with thorium nitrate, and also can also be utilized to test oxidants such as cost-free chlorine and chlorite.
  4. It is utilized to study its destruction making use of Fenton’s reagent. In microbiology, it is made use of to identify germs that generate secure acids via the mechanism of mixed-acid fermentation of sugar.

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Application of Methyl Red

Methyl red is a lustrous purple crystal or reddish-brown powder solid, and is one of the commonly used acid-base indicators. In the printing and dyeing industry, methyl red is widely used in the cloth dyeing and chemical industries because of its low price and easy preparation. Its application examples are as follows:

First prepare bromothymol blue methyl red mixed indicator, weigh 0.1g bromothymol blue, dissolve in 8.0ML sodium hydroxide solution with a concentration of 0.02Mol/L, and dilute to 250ML. Weigh 0.1g of methyl red, dissolve in 3.73ML of sodium hydroxide solution with a concentration of 0.02Mol/L, and dilute to 250ML. Mix the two solutions to prepare bromothymol blue methyl red mixed indicator. Take a 250mL glass Erlenmeyer flask, add 25mL of distilled water, and add 2 drops of bromothymol blue methyl red mixed indicator.

Connect a section of latex tube to the outlet of the sampling port valve measured by the device, pass the latex tube into the Erlenmeyer flask solution, open the gas valve, and feed tetrafluoroethylene gas at a rate of 500ml per minute for 2 minutes until the color of the solution is stable , you can determine the acidity and alkalinity of tetrafluoroethylene gas. The method of the invention is simple and convenient, and operators can quickly analyze the acidity of the tetrafluoroethylene gas on site.

The method comprises the following steps: preparing bromocresol green-methyl red indicator; taking a certain amount of NMP sample in a container, adding isopropanol and shaking it to make it evenly mixed; adding the bromocresol green-methyl red indicator Mix well, and titrate with hydrochloric acid standard solution, and the titration ends from green to slightly yellow; according to the formula: % free amine=c*V mark*K/ρ*V, calculate the % free amine in the NMP sample.

The present invention is by preparing bromocresol green-methyl red indicator, adopts the method for acid-base titration to test the content of amine in NMP, according to the parameter in the process of acid-base titration, expresses free amine content with mass percent: % free amine= c*V is marked with *K/ρ*V, and the performance of NMP is evaluated according to the test results. In addition, the test method is simple, convenient, quick and low in cost, and can be widely used in production and research.

First prepare 10%~90% ethanol solution; dissolve 0.07~0.12g methyl red in 100mL ethanol solution to obtain methyl red ethanol solution; take 0.08~0.15g bromothymol blue and dissolve it in 100mL ethanol solution to obtain bromine Thymol blue ethanol solution; mix 10~55mL methyl red ethanol solution with 15~50mL bromothymol blue ethanol solution, dilute 10 times to obtain indicator solution; add glycerin, heat in a constant temperature water bath, put in when the rated temperature is reached 1.2~2.2g methyl cellulose, stir continuously at high speed to form a uniform methyl cellulose solution; as the temperature drops, the viscosity of the solution increases; the indicator film solution is obtained; scrape the indicator film solution on cotton fiber paper , and dried under the blower to obtain a CO2 sensitive indicator label. This indicator label is suitable for rapid detection of CO2 content in the environment between 0% and 100%.

Difference Between Methyl Red and Methyl Orange

Acid-base indicators are generally organic weak acids or organic weak bases with complex structures, and their acidic forms and their conjugated basic forms have different colors. During the titration process, when the pH of the solution changes, the acid-base indicator loses a proton and changes from an acidic form to a basic form or gains a proton from a basic form to an acidic form, causing a change in structure, which is the color change principle of the indicator. When acid color and basic color account for half, pH=pKHIn (indicator constant), known as the theoretical color change point of the indicator.

The color change range of the indicator is the corresponding pH range from the beginning of the indicator to the end of the color change, which is pH=pKHIn±1. Due to the different sensitivity of human eyes to various colors, the acid color and basic color of the indicator also have the effect of covering each other. The acid-base indicator in the actual test will be affected by external factors, so the color change range will vary. The drop with the most obvious color change of the indicator within the range of color change is called the titration end point.

Methyl orange is formed by coupling p-aminobenzenesulfonic acid with N,N-dimethylaniline after diazotization. , Cr) and strong oxidants (chlorine, bromine) decolorizing indicator.

The discoloration range of methyl orange is red when the pH is ≤ 3.1, orange when the pH is 3.1~4.4, and yellow when the pH is ≥ 4.4.

It exists in the form of sulfonic acid sodium salt in neutral or alkaline solution, and is converted into sulfonic acid in acidic solution, so that the acidic sulfonic acid group forms p-dimethylaminophenyl with the basic dimethylamino group in the molecule The internal salt form of azobenzenesulfonic acid (p-quinone structure) becomes a conjugated system containing p-quinone structure, so the color changes accordingly.


  1. Methyl red – WikiPedia
  2. CN201810100857.9 A method for measuring the concentration of methyl red

Methyl Red Supplier and Manufacturer

As a methyl red supplier and manufacturer with a strict standard product quality system certificate, Zhishang Chemical has long been providing the best methyl red raw materials to customers all over the world.

Over the years, relying on professional team experience and customer-centric team concept to meet customer needs in a timely manner, our company enjoys a high reputation in the world. At present, our company has served more than 6,000 customers and has established long-term cooperative relations with customers from many countries.

If you have a demand for methyl red and related products, please contact our service staff Zhishang Chemical – White directly, and we will provide you with high-quality products at the best price.

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