Cresols (also hydroxytoluene) are organic compounds which are methylphenols. They are a widely occurring natural and manufactured group of aromatic organic compounds, which are categorized as phenols (sometimes called phenolics). Depending on the temperature, cresols can be solid or liquid because they have melting points not far from room temperature. Like other types of phenols, they are slowly oxidized by long exposure to air, and the impurities often give cresols a yellowish to brownish red tint. Cresols have an odor characteristic to that of other simple phenols, reminiscent to some of a "coal tar" smell. The name cresol reflects their structure, being phenols, and their traditional source, creosote.
In its chemical structure, a molecule of cresol has a methyl group substituted onto the ring of phenol. There are three forms (isomers) of cresol: ortho-cresol (o-cresol), meta-cresol (m-cresol), and para-cresol (p-cresol). These forms occur separately or as a mixture, which can also be called cresol or more specifically, tricresol. About half of the world's supply of cresols are extracted from coal tar. The rest is produced synthetically, by methylation of phenol or hydrolysis of chlorotoluenes.
Cresols are precursors or synthetic intermediates to other compounds and materials, including plastics, pesticides, pharmaceuticals, and dyes.
Derivatives of p-cresol include:Bupranolol, a non-selective beta blocker
Butylated hydroxytoluene, a common antioxidant
Indo-1, a popular calcium indicator
Derivatives of o-cresol include:MCPA, (4-chloro-2-methylphenoxy)acetic acid
MCPB, 4-(4-chloro-2-methylphenoxy)butanoic acid
Mecoprop, (RS)-2-(4-chloro-2-methylphenoxy)propanoic acid
the amine atomoxetine, (3R)-N-methyl-3-(2-methylphenoxy)-3-phenylpropan-1-amine
the diol mephenesin, 3-(2-methylphenoxy)propane-1,2-diol
Derivatives of m-cresol include:Amylmetacresol, an antiseptic
Chloro-m-cresol which is used as a household disinfectant
Most exposures to cresols are at very low levels that are not harmful. When cresols are inhaled, ingested, or applied to the skin at very high levels, they can be very harmful. Effects observed in people include irritation and burning of skin, eyes, mouth, and throat; abdominal pain and vomiting; heart damage; anemia; liver and kidney damage; facial paralysis; coma; and death.
Breathing high levels of cresols for a short time results in irritation of the nose and throat. Aside from these effects, very little is known about the effects of breathing cresols, for example, at lower levels over longer times.
Ingesting high levels results in kidney problems, mouth and throat burns, abdominal pain, vomiting, and effects on the blood and nervous system.
Skin contact with high levels of cresols can burn the skin and damage the kidneys, liver, blood, brain, and lungs.
Short-term and long-term studies with animals have shown similar effects from exposure to cresols. No human or animal studies have shown harmful effects from cresols on reproduction.
It is not known what the effects are from long-term ingestion or skin contact with low levels of cresols.
The Occupational Safety and Health Administration has set a permissible exposure limit at 5 ppm (22 mg/m3) over an eight-hour time-weighted average, while the National Institute for Occupational Safety and Health recommends a limit of 2.3 ppm (10 mg/m3).
A recent study, suggests that cresols are responsible for the formation of multiple sclerosis, in lab rats, at least. They are looking into the human connection as well.