Special gas chromatograph for alcohol substance detection

concept

Compounds containing hydroxyl groups that bind to the carbon on the alkyl or benzene ring side chains are called alcohols. Its functional group is - OH.

A class of organic compounds formed by the substitution of one or several hydrogen atoms with hydroxyl groups in hydrocarbon molecules. Compounds formed by replacing hydrogen on the ring of aromatic hydrocarbons with hydroxyl groups do not belong to alcohols but to phenols.

exist

There are many types of alcohols in nature, including ethanol and other alcohols in the same series in the fermentation broth. There are many terpene alcohols and aromatic alcohols in plant essence oil, which exist in free state or in the form of esters and acetals. There are also many alcohols present in the form of esters in animal and vegetable oils, fats, and waxes.

classification

According to the amount of hydroxyl groups contained, it can be divided into mono -, di -, tri -, or polyols. A carbon atom generally cannot contain two hydroxyl groups, and carbon diols are unstable and prone to dehydration, forming carbonyl compounds. Alcohols can also be classified into primary alcohols, secondary alcohols, and tertiary alcohols based on the number of hydrogen atoms on the carbon atom connecting the hydroxyl group.

name...as

There are generally three methods used: ① Common nomenclature, which considers alcohols as composed of two parts: alkyl and hydroxyl. The hydroxyl part is represented by the alcohol character, while the alkyl part removes the base character and is combined with the alcohol character. For example, n-butanol (primary alcohol) CH3CH2CH2OH, isobutanol (primary alcohol) (CH3) 2CHCH2OH, butanol (secondary alcohol) CH3CH2CH (OH) CH3, butanol (tertiary alcohol) (CH3) 3COH, and pentanol (primary alcohol) (CH3) 3C-CH2OH. ② Named after the source or characteristics of the alcohol, for example, xylenol (i.e. methanol) is obtained by dry distillation of wood, citronellol is obtained by reducing citral, orange blossom alcohol exists in orange blossom oil, and glycol (i.e. ethylene glycol) is named after its characteristics of alcohol and glycerol. ③ The system naming method involves selecting the longest carbon chain containing hydroxyl groups, calling it an alcohol based on the number of carbon atoms it contains, and numbering it sequentially from the end close to the hydroxyl group. When writing the full name, the number of the carbon atom where the hydroxyl group is located should be written before the alcohol, for example, 1-butanol CH3CH2CH2CH2OH. The position number and name of the side chain are written before the alcohol, such as 2-methyl-1-propanol. When naming multifunctional compounds containing hydroxyl groups, hydroxyl groups can be considered as substituents rather than alcohols.

nature

Generally, alcohols are colorless liquids or solids, monobasic alcohols with less than 12 carbon atoms are liquids, 12 or more are solids, and polyols (such as glycerol) are syrupy substances. Monohydric alcohols dissolve in organic solvents, while alcohols with less than three carbons dissolve in water. The melting and boiling points of lower alcohols are much higher than those of hydrocarbons with the same number of carbon atoms, due to the presence of hydrogen bonds in alcohol molecules that cause binding reactions. Saturated alcohols cannot cause bromine water to fade. Alcohols have active chemical properties, with both carbon oxygen and hydrogen oxygen bonds in the molecule being polar bonds. There are two main types of reactions that can occur with hydroxyl groups as the center: hydrogen oxygen bond cleavage and carbon oxygen bond cleavage. In addition, carbon atoms attached to hydroxyl groups are easily oxidized to form aldehydes, ketones, or acids.

Preparation method

Alcohol can be prepared by fermentation, for example, in China, sweet potatoes, potatoes, or other starchy substances are used for saccharification and fermentation to produce wine; It can also be prepared by chemical synthesis method. The commonly used methods in industry include reduction, hydration, oxidative synthesis, condensation reactions, and reduction of fats and oils. The spectral properties of alcohols in IR show two absorption peaks for - OH, ranging from 3640 to 3610 cm-1. The absorption band of unbound OH is sharp in shape. The absorption band of 3600-3200cm-1 bound OH is relatively wide in shape. The absorption peak of C-O is in the range of 1000-1200 cm-1. Primary alcohols are in the range of 1060~1030 cm-1, secondary alcohols are around 1100 cm-1, and tertiary alcohols are in the range of 1140 cm-1. In NMR, the nuclear magnetic resonance signal of O-H can exhibit a δ value in the range of 1~5.5 due to the influence of hydrogen bonding, temperature, solvent properties, etc. Low molecular weight alcohols are commonly used as solvents, antifreeze agents, extractants, etc; Advanced alcohols such as n-hexadecanol can be used as defoamers and evaporation inhibitors for reservoirs. Alcohol is still an extremely important chemical raw material.

Alcohol detection specific gas chromatograph