METHYL ORANGE: CHARACTERISTICS, SYNTHESIS AND APPLICATIONS - BIOLOGY - 2025

The methyl orange or methyl orange is an azo derivative compound used as a colorant and a pH indicator. Its scientific name is sodium salt of (p-azo] benzenesulfonic acid and its chemical formula C ₁₄ H ₁₄ N ₃ NaO ₃ S.

It is also known by other names such as: heliantine, Poivrier orange, III orange and gold orange. The color of methyl orange is orange-red. Its cornering zone ranges from 3.1 to 4.4. Below 3.1 it is red and above 4.4 it is yellow-orange.

Methyl orange. Source: Ben Mills

This azo-derived dye has various applications. These include: analysis of chemical and pharmaceutical substances, especially in the titration of acids and also as a colorant in textiles and biological fabrics.

This substance is a skin and mucous irritant. Therefore, safety implements should be used to handle this compound, such as a gown, gloves, closed shoes, and safety glasses. It also has mutagenic activity.

characteristics

The methyl orange pH indicator has a solid physical state and can be dissolved in water to form an aqueous solution. It is yellowish-orange in color and has no odor (odorless).

It has a boiling point at> 300 ° C, the density is equal to 1.28 g / cm ³. It is soluble in 500 parts of water and is insoluble in alcohol. Its molecular mass is 327.34 g / mol.

Synthesis

Obtaining methyl orange

The reaction comprises diazotization and dimethyl aniline coupling. For its synthesis we proceed as follows. The first thing is to prepare separately the following solutions:

Source: prepared by the author MSc. Marielsa Gil.

Process

When the solutions are cold, proceed as follows:

- Have an ice bath (between 0 and 5 ° C). On it, (1) add the solution (2) drop by drop, stirring frequently.

- In that temperature range (inside the ice bath), slowly add the solution (3), then add the solution (4).

- Remove from the ice bath and mix until it reaches room temperature. Little by little, the mixture will acquire a dark red color.

Then add 10% sodium hydroxide solution (NaOH) until reaching a slightly alkaline pH (approximately 40 ml). In case the solution is too dark, a little more 10% NaOH can be added until it takes on the characteristic color.

30 g of NaCL (common salt) is added and subjected to a heat source at 50 or 60 ° C. Let cool and filter by suction method. Expose for 10 minutes to a stream of air. Subsequently, the drying is finished using an oven or a desiccator, and finally it is weighed to determine the performance.

An aqueous solution of methyl orange can be prepared from the powder.

Applications

Analysis of chemical and pharmaceutical substances

Many chemicals require titration. The pH indicators help in this procedure. In this case, it is especially useful with acidic substances.

Dye in textile companies at 5%

Methyl orange, in addition to serving as a pH indicator, has the property of dyeing substrates such as cotton. That is why it is widely used in the textile industry.

Biological tissue stain

There are histological tissue staining techniques where a variety of stains are used, where Fuschin acid, methylene blue and gold orange or methyl orange participate.

With this technique, connective tissue and collagen are stained dark blue, muscle tissue is colored bright orange, while chromatin is stained yellowish-brown, and erythrocytes are stained orange-red.

Toxicity

The methyl orange pH indicator is toxic, therefore direct contact with skin and mucous membranes should be avoided. It is also toxic by inhalation or ingestion. In all the mentioned cases it has an irritating effect, being able to redden the affected area.

The NFPA (National Fire Protection Association) classifies substances according to 3 categories identified by color: health hazards (blue), flammability (red), and radioactivity (yellow). Each one is weighted with a numbering ranging from 0 to 4.

According to the NFPA this substance was classified as a health risk 2, which means moderate risk. Regarding flammability it is classified as 1, which means slight risk; and in terms of reactivity it is classified as 0, that is, there is no risk of this nature.

Impact on the environment

The methyl orange pH indicator can be toxic to the environment, therefore, its waste must be disposed of in accordance with the provisions of the laws of each country.

Its waste is found in effluents from textile industries, which use this dye to dye fabrics, paper, and leather, among other products.

The maximum allowed limit is 200 mg / L in total suspended solids of dyes.

The absorption technique today is seen as one of the best options to remove organic compounds from water.

For this reason, research is being done to remove the methyl orange dye among other organic compounds with low-cost absorbent materials, such as: orange peel, cotton, rice, activated carbon, bentonite, powdered leaves, coconut shell, charcoal. sawdust, ZnO nanoparticles and lamellar double hydroxides.

First aid

In the event of some type of accident with this substance, proceed as follows:

- If the methyl orange pH indicator splashes on the ocular mucosa, it should be rinsed with plenty of cold water for 15 minutes.

- In case of direct skin contact, rinse with plenty of water and then treat the irritation with an anti-inflammatory cream.

- If it splashes on clothing or shoes, these must be removed and washed before reuse.

- In case of inhalation, move the patient to a place with plenty of fresh air. If he has difficulty breathing, assist him with artificial respiration, and if possible oxygen should be administered.

- Finally, if the substance was ingested, you should not induce vomiting, and it is necessary to drink plenty of water. In all cases, medical assistance should be sought immediately.

References

1. Ramírez L, Jacobo A, Martínez M. Adsorption of methyl orange in aqueous solution on laminar double hydroxides. Acta univ, 2015; 25 (3): 25-34. Available at: scielo.org.
2. "Methyl orange." Wikipedia, The Free Encyclopedia. 2 Apr 2019, 22:21 UTC. 18 May 2019, 16:29. es.wikipedia.org/
3. National Institute of Rehabilitation Biosafety Committee, Safety Sheet. Methyl orange. 2013.Available at: inr.gob.mx
4. Safety Sheet Methyl Orange MSDS. University of Heredia, School of Chemistry. Costa Rica. Available at: Users / Team / Downloads
5. Vogel A. Vogel's. Textbook of Practical Organic Chemistry 5th Edition, Longman, pp 951
6. Wikipedia contributors. "Methyl orange." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, Jan 17, 2019. Web. May 19 2019.
7. Zyoud A, Zu'bi A, Helal MH, Park D, Campet G, Hilal HS. Optimizing photo-mineralization of aqueous methyl orange by nano-ZnO catalyst under simulated natural conditions. J Environ Health Sci Eng. 2015; 13: 46.
8. Microscopy Fuchsin acid. 2017. Available in: Users / Team / Download.