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Organic Functional Group Analysis

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  • Organic Functional Group Analysis

    Functional groups are atoms or atomic groups that determine the chemical properties of organic compounds. Common functional groups include hydroxyl group, carboxyl group, ether bond, aldehyde group, carbonyl group and so on. Organic chemical reactions mainly occur in functional groups, which play a decisive role in the properties of organic compounds. Functional groups such as -X,-OH,-CHO,-COOH,-NO2,-SO3H,-NH2 and RCO-, determine the chemical properties of halogenated hydrocarbons, alcohols or phenols, aldehydes, carboxylic acids, nitro compounds or nitrites, sulfonic acids, amines and amides.

    As a professional reliability third-party testing organization, T,C&A Lab can provide testing and quantitative analysis of organic functional groups. Welcome to contact our experts for consultation.

    Testing of organic functional groups

    • Alkane testing
    • Generally speaking, there is no suitable qualitative test method for alkanes, but it is inferred from the results of element qualitative analysis and solubility test that the identification is mainly based on physical constants (boiling point, density, refractive index, etc.) and spectral characteristics.

    • Testing of olefins and alkynes
    • Olefins and alkynes are similar in physical state to alkanes. Due to the decrease in the number of double bonds and hydrogen in structure, burning often brings black smoke. Olefins and alkynes are only soluble in concentrated H2SO4 and belong to N group.

      Common testing methods: carbon tetrachloride test of bromine and potassium permanganate test.

    • Halogenated hydrocarbon testing
    • In addition to C1~C2 chloroalkane and C1 bromide, halogenated hydrocarbons are colorless liquids (except fluoroalkanes). Most aromatic halides are colorless liquids with aromatic odors.

      If the element qualitative analysis already knows that the compound molecule contains halogen, it can be inferred which type of halide it is through the silver nitrate alcohol solution test and the sodium iodide-acetone solution test.

    • Testing of organic oxygen-containing compounds
      • Testing of alcohol compounds
      • The characteristic functional group of alcohols is hydroxyl. According to the hydroxyl groups attached to different carbon atoms, they can be divided into primary, secondary and tertiary alcohols. According to the number of hydroxyl groups in the molecule, there are also monohydric, dihydric and polyhydric alcohols. So, first check whether it has an alcoholic hydroxyl group, and then distinguish primary, secondary, tertiary alcohol, and whether it is a polyhydric alcohol.

      • Testing of phenolic compounds
      • Phenols are solid except m-phenol and m-substituted halogenated phenol. Monophenols have a strong smell. In addition to nitrophenol, most pure phenols should be colorless, and the color of phenol bands is often caused by oxidation. The solubility of monophenol in water is very small, and with the increase of hydroxyl groups on the benzene ring, the solubility in water increases.

        Ferric trichloride test and bromine water test are commonly used in the testing of phenol.

      • Testing of carbonyl compounds
      • Carbonyl compounds include aldehydes and ketones. Since both aldehydes and ketones have carbonyl groups, they can undergo addition condensation reactions with carbonyl reagents. For example, they can react with hydroxylamine to form oximes and condense with hydrazine to form hydrazones. Aldehydes are easily oxidized by weak oxidants due to the active hydrogen attached to the carbonyl group, which distinguishes aldehydes from ketones.

      • Testing of carboxylic acids and their derivatives
      • The unitary fatty acids below C2 are liquid, while binary or polycarboxylic acids and aromatic acids are solid. The mononic acid of C1~C2 has a strong irritating sour taste, C4~C6 acid has an unpleasant smell, and the unpleasant smell of acid above C7 decreases gradually. C1~C4 monocarboxylic acid is soluble in water and also in ether. Lower binary and polyacids are soluble in water, but insoluble in ether.

        Test methods for carboxylic acids include: potassium iodate-potassium iodide test, and iron hydroxamate test.

        Carboxylic acid derivatives, such as esters, acyl halides, anhydrides and amines, can produce corresponding hydroxamic acids, and their existence is tested by iron hydroxamic acid test.

      • Testing of organic nitrogen-containing compounds
        • Testing of amine compounds
        • A nitrogen-containing compound, if its aqueous solution is alkaline, or its solubility in hydrochloric acid is greater than its solubility in water, or its aqueous solution contains halogen ions or other acid radical ions, then the compound may be an amine or its salt. The question left is to determine whether it is a primary, secondary or tertiary amine, which is usually determined by the Hinsberg test and the nitrous acid test.

        • Testing of nitro compounds
        • Nitroalkanes and nitroaromatic hydrocarbons can be judged not only from simple physical properties and appearance, but also from acidic groups (primary and secondary nitro compounds have weak acidic groups). However, many nitro compounds can be neutral in ferrous hydroxide test and sodium hydroxide acetone test.

    • Testing of organic sulfur compounds
    • The common sulfur compounds are mercaptan, thiophenol, thioethers, xanthamides and so on.

      • Testing of mercaptan and thiophenol
      • Most of these compounds are liquids, have an extremely bad smell and have little solubility in water. All of them are soluble in 5%NaOH solution but insoluble in 5%NaHCO3. Mercaptan and thiophenol react with sodium lead to form yellow lead salt. if they interact with sulfur, lead sulfide black precipitates can be formed.

      • Testing of sulfonic acids
        • Sodium hydroxide-nickel hydroxide test
        • Sodium bisulfite is formed when sulfonic acid and sodium hydroxide are eutectic
        • The reaction product is acidified with hydrochloric acid, that is, sulfur dioxide is released. When sulfur dioxide meets the filter paper coated with nickel hydroxide, it reacts to produce black NiO(OH)2
        • Black NiO(OH)2 turns blue when it meets with acetic acid benzidine
        • Other sulfides such as thiourea and sodium hydroxide eutectic to generate sodium sulfide, acidification to generate hydrogen sulfide, and Ni(OH)2 to generate black NiS, and do not react with benzidine acetate, which is different from copper sulfonic acid.
        • Sulfuramide can also be tested by this method and distinguish it from other sulfides

    Quantitative analysis

    Quantitative analysis of functional groups mainly solves two problems:

    Through the quantitative determination of the characteristic functional groups of a component in the sample, the percentage content of a component in the sample was determined.

    Through the quantitative determination of the characteristic functional groups of a substance, the percentage and number of characteristic functional groups in the molecule are determined, so as to determine or verify the structure of the compound.

    The quantitative analysis of organic functional groups can be divided into chemical method and instrument method.

    • Chemical method
    • The chemical method is carried out by measuring the consumption of reagents or the formation of one of the reaction products by using the characteristic chemical reactions of functional groups. The substances measured include acids, bases, oxidants, reducing agents, moisture, precipitates, gases or colored substances, etc.

      • Acid-base titration
      • Redox titration
      • Precipitation titration
      • Moisture determination method
      • Gas measurement method
      • Colorimetric analysis
    • Instrument method
      • Ultraviolet-visible spectrophotometry
      • All organic compounds containing conjugated unsaturated bonds or aromatic rings in the molecule have characteristic absorption in the ultraviolet region (200-400 nm).

      • Infrared spectroscopy
      • Organic functional groups have characteristic infrared absorption. For example, the characteristic absorption of ketone group is 1725 1700 cm-1, and the characteristic absorption of methyl group is 1385~1370 cm-1. At the characteristic absorption, the functional group can be measured by infrared spectroscopy according to the Lambert-Beer law.

      • NMR spectroscopy
      • Proton magnetic resonance spectroscopy (see NMR) is usually used for the quantitative analysis of organic functional groups. The chemical shift and coupling constant on the spectrum are qualitative indexes, while the absorption peak area is quantitative index. It directly reflects the number of these protons and is proportional to the concentration of the sample.

      • Other methods
      • In addition, we also use mass spectrometry, chromatography, chromatography-mass spectrometry, electrochemical analysis and other methods for the quantitative analysis of functional groups.

    Instruments and data

    Organic Functional Group Analysis
    Organic Functional Group

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