Questions and Answers
What is the primary use of alkaloidal precipitating agents?
Which of the following is NOT a disadvantage of using precipitating agents for alkaloids?
Which reagent is classified as a halogen-containing precipitating agent?
What type of chemical compound does Hager's Reagent represent?
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Which method employs alkalis for the extraction of alkaloids?
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In which of the following methods are alkaloids extracted with water immiscible organic solvents?
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Which of the following reagents is NOT a qualitative test for alkaloids?
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Which reagent is formed by combining formaldehyde and concentrated sulfuric acid?
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Which amino acid is NOT typically a precursor for alkaloids?
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What is the primary purpose of acidifying an extract during the purification of crude alkaloidal fractions?
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Which method is NOT typically used for the identification of alkaloids?
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What structural feature is common among alkaloids?
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Which alkaloid structure is associated with tropane?
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What is the outcome of repeated acid-base procedures in alkaloid extraction?
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Which of the following is a characteristic property determined during the identification of alkaloids?
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The precursor amino acid tryptophan is primarily associated with which alkaloidal structure?
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Who coined the term 'alkaloid'?
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Which alkaloid was isolated first in the early 19th century?
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In which part of the plant is coniine typically found?
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Which family is known to be rich in alkaloids?
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What is one of the functions of alkaloids in plants?
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Which alkaloid was discovered last among those listed in the early 19th century?
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What role do alkaloids serve in cases of nitrogen deficiency?
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Which of the following families is free from alkaloids?
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Study Notes
Brief History of Alkaloids
- The term alkaloid was introduced by A. Meissner in 1819.
- Alkaloids serve various roles such as poisons, medicines, and stimulants.
- French chemists Derosne (1803) isolated narcotine, while Sertürner isolated morphine (1806, 1816).
- Key discoveries in early alkaloid chemistry include quinine (1820) and strychnine (1818) by Pelletier and Caventou.
- Caffeine was identified in 1820, along with other alkaloids like nicotine (1828) and cocaine (1860).
- Coniine was the first alkaloid to have its structure established (1870) and synthesized (1889).
Occurrence in Plants
- Alkaloids are rare in lower plants and are more abundant in dicots than in monocots.
- Rich sources of alkaloids include the families: Apocynaceae, Rubiaceae, Solanaceae, and Papaveraceae.
- Families typically lacking alkaloids include Rosaceae and Labiatae.
Distribution of Alkaloids
- Present in various plant parts, including:
- All parts: Example - Datura
- Barks: Example - Cinchona
- Seeds: Example - Nux vomica
- Roots: Example - Aconite
- Fruits: Example - Black pepper
- Leaves: Example - Tobacco
- Latex: Example - Opium
Function in Plants
- Alkaloids serve as protective agents against herbivores due to their bitter taste and toxicity.
- They can signify the end products of detoxification or function as a nitrogen source.
- Act as growth regulators and energy sources under nutrient deficiencies.
- Typically water-insoluble and can create precipitates to indicate alkaloid presence in tests.
Alkaloidal Precipitating Agents
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Double salt reagents include:
- Mayer’s Reagent: Potassium Mercuric Iodide.
- Dragendorff’s Reagent: Potassium Iodobismethate.
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Halogen-containing reagents:
- Wagner’s Reagent: Iodine/Potassium Iodide.
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Organic acids such as:
- Hager’s Reagent: Picric Acid and Tannic Acid.
- Oxygenated high molecular weight acids include phosphomolybdic and phosphotungestic acids.
Qualitative Tests for Alkaloids
- Common color reagents include:
- Froehd’s Reagent: Phosphomolybdic acid.
- Marqui’s Reagent: Formaldehyde with concentrated sulfuric acid.
- Erdmann’s Reagent: Concentrated nitric and sulfuric acids.
Extraction and Isolation of Alkaloids
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Extraction methods:
- Method I: Use of alkalis with water-immiscible solvents.
- Method II: Extraction using dilute acid in aqueous alcohol.
- Method III: Water-soluble organic solvents like methanol or ethanol.
- Repeated acid-base procedures help purify alkaloids by selectively dissolving impurities using organic solvents.
Identification Techniques for Alkaloids
- Melting point determination and color tests assist in identifying alkaloids.
- Advanced methods include HPLC, GC, GC-MS, UV, IR, NMR, and MS.
Alkaloid Biosynthesis
- Alkaloids are synthesized from amino acids and other plant amines.
- Key amino acids involved in alkaloid formation include phenylalanine, tyrosine, tryptophan, histidine, lysine, and ornithine.
- Other biochemical precursors, such as terpenes or steroids, may contribute to the alkaloidal skeleton.
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Description
Explore the fascinating history of alkaloids, from their introduction by A. Meissner in 1819 to significant discoveries by French chemists like Derosne and Sertürner. This quiz covers the roles, isolation, and identification of important alkaloids such as morphine, quinine, and caffeine.
