Question

Phenols can act as antioxidant because.
a) They are acidic.
b) they undergo electrophilic substitution.
c) they are free radical scavengers
d) they are easily oxidize

Answer 1

Answer:

because they are acidic .....

Answer 2

Correct answer is C ) . They are free radical scavengers

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★ The property of antioxidant in phenols is due to the free radical scavenging.

• Phenols has ability to mop up free radicals and to express them inactive what we called free radical scavenging .

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★ About phenols →

• Phenol (phenol), the general formula is ArOH, is a type of aromatic compound in which the hydrogen on the aromatic hydrocarbon ring is replaced by a
• hydroxyl group (—OH). The simplest phenol is phenol . Phenolic compounds refer to compounds produced by the substitution of hydrogen atoms on the benzene ring of aromatic hydrocarbons with hydroxyl groups, and can be divided into monohydric phenols and polyhydric phenols according to the number of hydroxyl groups contained in their molecules.

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★ Phenolic compounds

It is a hydroxyl-containing derivative of aromatic hydrocarbons , which is divided into volatile phenol and non-volatile phenol according to its volatility. Most of the phenolic compounds present in nature are the result of plant life activities. The phenol contained in plants is called endogenous phenol, and the rest are called exogenous phenols. Phenolic compounds all have a special aromatic odor, are weakly acidic, and are easily oxidized in the environment. Phenol and cresol have the highest content in phenol-containing wastewater . Therefore, environmental monitoring often uses volatile phenols such as phenol and cresol as pollution indicators.

Phenol pollution in the environment mainly refers to the pollution of phenolic compounds to water bodies. Phenol-containing wastewater is one of the most harmful and extensively polluted industrial wastewater in the world today, and is an important source of water pollution in the environment . In many industrial fields such as coal gas, coking , oil refining , metallurgy, machinery manufacturing, glass, petrochemicals, wood fiber, chemical organic synthesis industry, plastics, medicine, pesticides, paints and other industries, wastewater contains phenol. If these waste waters are not directly treated and directly discharged or irrigated, they can pollute the atmosphere, water, soil and food.

Phenol is a medium-strength chemical poison that chemically reacts with proteins in cell plasma. At low concentrations it denatures the cells and at high concentrations it coagulates the protein. Phenolic compounds can enter the body through the skin, mucous membranes, respiratory tract and digestive tract. Low concentration can cause cumulative chronic poisoning, and high concentration can cause acute poisoning and cause coma death. Generally speaking, after phenol enters the human body, the body is converted into non-toxic substances by its own detoxification function and discharged from the body. Only when the intake exceeds the detoxification function will it accumulate and lead to chronic poisoning , manifested by dizziness, headache, restlessness, loss of appetite, vomiting and diarrhea.

Since phenol is extremely versatile, it is difficult to prevent pollution. In factories that produce and use phenol, a strict operating system must be established to guard against the diarrhea of phenol. At the same time, it is necessary to do a good job in the recycling and biological oxidation of wastewater, and it is strictly prohibited to discharge phenol-containing wastewater into infiltration wells and infiltration pits, so as not to pollute the groundwater.

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★ Identification of phenolic compounds

Ferric chloride test:

• Take 1ml of the aqueous solution of the test product, add 1-2 drops of the ferric chloride test solution, and it will show green, dirty green, blue black or dark purple (hydro-lyzable tannin shows blue to blue black, condensation tanning Show green and pollute green).
• Tannins are derivatives of poly-hydric phenols, that is, poly-hydric phenols, which can react with ferric ions to produce complex complex salts .
• Note → This reaction can hinder the formation of color in the presence of mineral acid, organic acid, acetate, etc. Nitro-phenols have no obvious reaction to ferric chloride reagent.

Gelatin test:

• Take 1ml of the aqueous solution of the test product, add 2-3 drops of sodium chloride gelatin solution, and a white precipitate will be generated.
• Tannin has the properties of coagulated protein.

Bromine test:

• Take 1 ml of the aqueous solution of the test article, add 1-2 drops of the bromine test solution, and generate a white or precipitate, indicating that it may contain phenol or catechol tannin.
• Note → Too much bromine will hinder the precipitation of tannin, so bromine water should not be added.

Vanillin mono-acid test:

• Take the aqueous solution of the test sample on the filter paper, after drying, spray or drop vanillin mono-hydrochloric acid test solution, showing red spots (polyphenols).

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Tannins , phenolic TLC detection reaction:

• Adsorbent: polyamide ; silica gel; silica gel; gypsum: water (5: 1: 7) is adjusted into a shape, coated into a thin plate, and dried at 1050k for 45 minutes.