Hydroquinone

The Properties and Uses of Hydroquinone

Manufactured in the form of an antioxidant, inhibitor, and even an intermediate in the procedure of synthesizing motor fuels, oils, and dyes, Hydroquinone is a phenol derivative. It occurs naturally in different species of plants and is also used in photographic processing. The antioxidant properties of this compound can result in toxicity of several organs, especially the kidney. Hydroquinone is even used for treating skin hyperpigmentation. It is one of the main ingredients in different cosmetic products. The compound is mainly metabolized to the conjugates of glutathione. Thus, it forms the adducts of mutagenic DNA in in-vitro mechanisms. It was Friedrich Wohler who coined the name Hydroquinone in the year 1843.


Understanding What is Hydroquinone Exactly?

Coming to getting the exact answer to the question, what is Hydroquinone? The answer is this compound is also called benzene-1, and it is a 4-diol aromatic natural; compound and a kind of phenol. Hydroquinone formula is C6H6O2, and it is widely used in the form of a biomarker for benzene exposure. In normal people, Hydroquinone is available from the catabolism of substrates like tyrosine. Others come through gut bacteria, dietary ingestion, cigarette smoking, and ingestion of foods that contain arbutin. The use of different over-the-counter medications can also result in Hydroquinone's presence in the normal human body.


The Structure of Hydroquinone

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Hydroquinone structure features a couple of hydroxyl groups linked to one benzene ring in the para position. The compound appears as a granular solid in white color under pressure and at room temperature. The groups of hydroxyls found in the structure of Hydroquinone tend to be weakly acidic. The compound can lose one H+ from one of its hydroxyls and form a mono-phenolate ion. It can even lose an H+ from both for forming a phenolate ion. 

This melanin synthesis inhibitor, which is also called Quinol or 4-diol, has an assortment of uses. Hydroquinone's uses are generally associated with the way it acts when used in the form of a water-soluble reducing agent. Hydroquinone is one of the most important components of photographic developers, consisting of a compound called Metol. Hydroquinone can reduce silver halides to fundamental silver.

There are different procedures used for manufacturing Hydroquinone. But the most extensively used industrial processes are cumene and phenol hydroxylation. Then there are less-popular methods of producing Hydroquinone. These include oxidation of different phenols, dry distillation of quinic acid, oxidation of aniline by manganese dioxide, and from the use of iron pentacarbonyl and acetylene. The compound does not only appear naturally in different plant species but even in the defensive glands of the bombardier beetles.


Hydroquinone Properties

The physical and chemical properties of Hydroquinone are as follows:

  • Chemical formula: C₂H₆O₂

  • Density: 1.3 g cm⁻³

  • Molar Mass or Molecular weight: 110.11 g/mol

  • Melting point: 172 degrees C

  • Boiling point: 287 degrees C


Uses of Hydroquinone

Hydroquinone Uses Include:

  • Hydroquinone is used in the form of a reducing agent.

  • The compound can be highly effective in the treatment of melasma.

  • Hydroquinone is also used for treating acne scars.

  • It can also be used for preventing methyl methacrylate.

  • Hydroquinone serves as one of the most common and active ingredients in different cosmetic products.

  • It can help with skin whitening.

  • Hydroquinone is also used in the form of a biomarker in benzene exposure.

  • The compound can also be found in photographic developers.


Hydroquinone Side Effects

Though Hydroquinone has many effective uses, there are even some side effects of using the compound. The side effects are as follows:

  • Stinging

  • Mild burning

  • Dryness

  • Redness of the skin.

These are some common side effects of using Hydroquinone. They might go away on their own, but if they persist and worsen with time, the immediate help of a healthcare professional is recommended. Other serious side effects of using Hydroquinone as medicine include:

  • Skin cracking

  • Blistering

  • Blue or black darkening of the skin

Allergic reactions to Hydroquinone are quite rare, but symptoms like itching, swelling, rash, trouble breathing, and severe dizziness need to be dealt with promptly.


Precautions to have in Mind

You must always consult a pharmacist or a doctor before using this compound as it can have serious side effects and cause allergies. It contains certain inactive ingredients like sulfites that can result in allergies and other problems. Pregnant women should avoid the use of Hydroquinone, and if they require it, they must have a word with their health care provider.

FAQ (Frequently Asked Questions)

1. What are Hydroquinone Alternatives, and is Oxidized Hydroquinone Effective?

One of the most common alternatives to Hydroquinone is Mequinol or 4-Hydroxyanisole. It is also called monomethyl ether, methoxyphenol with Hydroquinone, along with p-hydroxyanisole. Studies suggest that Mequinol is effective and works the same as Hydroquinone.


Whether oxidized Hydroquinone is effective or not? The answer is oxidized Hydroquinone is not effective in any way, and it is also not harmful. Oxidized Hydroquinone turns brown, and it is better not to use it for different activities.

2. Can Hydroquinone be Used for a Long Term Safely?

There are some adverse effects of using Hydroquinone for a very long time. The complications include discolouration of fingers, Ochronosis, Cornea degeneration, and conjunctival melanosis. In this context, Ochronosis is one of the most prevalent medical conditions caused by the long-term usage of Hydroquinone.


Prescribed concentrations of this compound are generally less than 4%. Patients taking Hydroquinone should not expose themselves to sunlight. At most, Hydroquinone can be taken for four to five months, not more than that. Hydroquinone therapy also requires going through a period of complete skin relaxation once the therapy is complete. This skin relaxation period generally spans over two to three months. The use of Hydroquinone for a very long time is not recommended by doctors, mainly because of the antioxidant properties of the compound. Nevertheless, it is safe to use the compound for a short period.