In the process of drug production, research and inspection, problems such as separation, purification and identification of organic compounds are often encountered. The identification, separation and purification of organic compounds are three related but different concepts.
The purpose of separation and purification is to obtain pure substances from the mixture, but the requirements are different and the processing methods are also different. Separation is the separation of the individual components of a mixture. In the separation process, a certain component in the mixture is often converted into a new compound through a chemical reaction, and it is also reduced to the original compound after separation. There are three cases of purification, one is to try to convert the impurities into the desired compounds, the second is to convert the impurities into another compound through appropriate chemical reactions to separate them (the separated compounds do not have to be reduced again), the third It is separated by physical methods (liquid separation, chromatography, etc.).
Identification is based on the different properties of a compound to determine what functional group it contains and which compound it is. For example, to identify a group of compounds, it is enough to determine which compound each is.
Qualified
When doing identification questions, it should be noted that not all chemical properties of compounds can be used for identification, and certain conditions must be met:
(1) There is a color change in the chemical reaction;
(2) The chemical reaction process is accompanied by obvious temperature changes (exothermic or endothermic);
(3) The reaction product produces gas;
(4) The reaction products include the formation of precipitation or the dissolution of precipitation during the reaction process, and the stratification of products.
Specific method
1. Unsaturated bonds:
(1) Bromine in carbon tetrachloride solution, the red color fades. Misjudgment: Bromine is extracted.
(2) Potassium permanganate solution, the purple color fades.
2. Alkynes containing alkyne hydrogens:
(1) Silver nitrate, resulting in a white precipitation of acetylenic silver.
(2) Ammonia solution of cuprous chloride produces red precipitation of cuprous acetylide.
3. Small cyclic hydrocarbons: Four-membered alicyclic hydrocarbons can make the solution of bromine in carbon tetrachloride become discolored.
4. Halogenated hydrocarbons: the alcohol solution of silver nitrate generates silver halide precipitation; halogenated hydrocarbons with different structures generate precipitation at different speeds, tertiary halogenated hydrocarbons and allylic halogenated hydrocarbons are the fastest, followed by secondary halogenated hydrocarbons. Primary halogenated hydrocarbons require heating to precipitate. You can tell which halogen it is based on the color of the precipitate.
5. Alcohol:
(1) Reaction with metallic sodium to release hydrogen (identification of alcohols with less than 6 carbon atoms).
(2) Using Lucas reagent to identify primary, secondary and tertiary alcohols, the tertiary alcohols become cloudy immediately, the secondary alcohols become cloudy after being placed, and the primary alcohols are unchanged after being placed.
(3) The vicinal diol reacts with copper ions to produce a magenta-blue precipitate.
6. Phenolic or enol compounds:
(1) Use ferric chloride solution to produce color (phenol produces blue-violet).
(2) Phenol and bromine water form a white precipitate of tribromophenol.
7. Carbonyl compounds:
(1) Identify all aldehydes and ketones: 2,4-dinitrophenylhydrazine, which produces a yellow or orange-red precipitate. Grignard reagents can also be used.
(2) Doran's reagent is used to distinguish aldehydes from ketones. Aldehydes can generate silver mirrors, but ketones cannot.
(3) To distinguish between aromatic aldehydes and aliphatic aldehydes or ketones and aliphatic aldehydes, using Fehling's reagent, aliphatic aldehydes produce brick red precipitates, but ketones and aromatic aldehydes cannot.
(4) To identify methyl ketone and alcohol with structure, use iodine in sodium hydroxide solution to generate yellow iodoform precipitation.
8. Formic acid:
With silver ammonia solution, formic acid can generate silver mirrors, while other acids cannot.
9. Amines: There are two ways to distinguish primary, secondary and tertiary amines:
(1) Use benzenesulfonyl chloride or p-toluenesulfonyl chloride to react in NaOH solution, the product generated by primary amine is soluble in NaOH; the product generated by secondary amine is insoluble in NaOH solution; tertiary amine does not react.
(2) With NaNO2+HCl:
Fatty amines: primary amines emit nitrogen gas, secondary amines generate yellow oil, and tertiary amines do not react.
Aromatic amines: primary amines form diazonium salts, secondary amines form yellow oils, and tertiary amines form orange-yellow (acidic conditions) or green solids (basic conditions).
10. Sugar:
(1) Monosaccharides can interact with Tollen's reagent and Fehling's reagent to produce silver mirror or brick red precipitate.
(2) Glucose and fructose: Glucose and fructose can be distinguished by bromine water. Glucose can make bromine water fade, but fructose cannot.
(3) Maltose and sucrose: with Tollen's reagent or Fehling's reagent, maltose can produce silver mirror or brick red precipitate, but sucrose cannot.
