[Chemistry Class Notes] Naphthol Pdf for Exam

Have you ever stepped into an elderly person’s closet and detected a peculiar and pungent odor right away? It’s a distinct smell that younger generations aren’t familiar with, as the substance that emits it has been phased out in recent years. You may wonder what’s causing the odor. It’s known as mothballs. Mothballs were used in clothes as a fumigant to prevent moths and other insects from destroying the textiles.

Naphthalene, a polyaromatic hydrocarbon, is the primary ingredient in conventional mothballs. Polyaromatic denotes the presence of more than one benzene ring, while hydrocarbon denotes the presence of only carbon and hydrogen atoms. Today, we’ll hear about naphthol, a naphthalene derivative. Naphthol is very similar to its parent compound, naphthalene, with the exception of the hydroxyl (-OH) group. Let’s take a look at some of this molecule’s main features together!

Amino Naphthol

Naphthol is one of two colorless, crystalline organic compounds derived from naphthalene and belonging to the phenol family; the molecular formula for both is C10H7OH. Both compounds have long been associated with the production of dyes and dye intermediates, but they also have significant applications in other industries.

The compound 1-naphthol, or alpha naphthol, is used directly in some dyes and is converted to compounds that are eventually integrated into other dyes. Heating 1-naphthalenesulfonic acid with caustic alkali or heating 1-naphthalene amine with water under pressure produces it.

The compound 2-naphthol, also known as b naphthol, is the most common naphthalene-based chemical intermediate. It’s made by combining 2-naphthalenesulfonic acid and caustic soda, and it’s used to make a variety of dyes and dye intermediates, as well as tanning agents, antioxidants, and antiseptics. It has been shown to cause cancer.

Structure

A hydroxyl group is bonded to a naphthalene ring to form naphthol. 1-naphthol and 2-naphthol are two isomers of naphthol (compounds with the same chemical formula but different atom connectivity). The hydroxyl group is bound to a different carbon in the naphthalene ring in the two isomers.

Aromaticity is another significant structural characteristic of naphthol. It has alternating double and single bonds in its rings, which is typical of aromatics.

Polarity

Since it comprises a hydroxyl group, naphthol is a strongly polar molecule, with the oxygen atom attracting electron density to itself through the bonds. A difference in electronegativity (an atom’s ability to attract electrons) between one or more atoms is needed for a molecule to be polar, and oxygen is more electronegative than both carbon and hydrogen in the case of naphthol. As a result, it can ‘hog’ more electron density in the form of bonds, causing it to become polar.

Solubility

Naphthol is very flexible in terms of the solvents it is soluble in (things in which it can form solutions). It can make a hydrogen bond with other alcohol-based (polar) solvents including ethanol, methanol, and isopropanol due to the presence of the hydroxyl group. Because of its ability to form hydrogen bonds, it is easily soluble in these types of solvents.  

Alcoholic Alpha Naphthol

Molisch’s test is a biochemical test for detecting the presence of carbohydrates in solution, named after the Austrian chemist H. Molisch (1856–1937), who invented it. A small amount of alcoholic alpha-naphthol is applied to the test solution, followed by a gradual pour of concentrated sulphuric acid down the test tube’s rim. The creation of a violet ring at the junction of the two liquids indicates a positive reaction.

Pyridylazo Naphthol

The orange dye pyridylazo-2-naphthol (PAN) is widely used as an acid-base indicator. Since it can form chelates with metal ions, it’s a good indicator for complexometric titrations. PAN may also be used as a spectrophotometric reagent to remove metal chelates from an organic solvent.

Furfural and 1 Naphthol

The rapid furfural test is similar to Molisch’s test, except that concentrated hydrochloric acid is used instead of concentrated sulfuric acid, and the solution is boiled. To ethanolic 1-Naphthol and concentrated hydrochloric acid, a dilute sugar solution is added.