Dragendorff's reagent is a color reagent to detect alkaloids in a test sample or as a stain for chromatography plates. Alkaloids, if present in the solution of sample, will react with Dragendorff's reagent and produce an orange or orange-red precipitate. [1] This reagent was invented by the German pharmacologist, Johann Georg Dragendorff (1836–1898) at the University of Dorpat. [2]
Dragendorff's reagent is prepared by mixing a concentrated solution of potassium iodide with a solution of bismuth subnitrate in a diluted acid (acetic acid or tartaric acid, hydrochloric acid or sulfuric acid is rarely being used) as a low pH is mandatory for this reagent. [2]
The formation is as follows:
The black precipitate of bismuth iodide is formed from the reaction of bismuth ion and potassium iodide.
Then, the reaction between bismuth ion and excess potassium iodide will produce a soluble complex of potassium tetraiodobismuthate which has an orange color.
Many compositions degrade over time and are sensitive to light, so for long-term storage it is often prepared as two separate solutions to be mixed before use, one containing bismuth subnitrate and acid with the other containing potassium iodide.
The most common composition is as follows:
Part A: 0.85g bismuth subnitrate, 40mL water, and 10mL glacial acetic acid.
Part B: 8g potassium iodide and 20mL water.
There are many different compositions in literature for the combined reagent. Some combine the entire volume of both solutions without dilution, but most involve diluting equal parts of these solutions with acid and water. One common composition is 5mL each of part A & B with 20mL of glacial acetic acid and 70-100mL of water. [2]
Most of the alkaloids have a tertiary amine group, so the explanation for color reaction could be the following:
Then the insoluble complex salt is formed from the reaction between ammonium salt and potassium tetraiodobismuthate.
This ion pair has different colors: yellow, orange, red, and brown, which depend on the nature of alkaloids. [2]
Iodine is a chemical element; it has symbol I and atomic number 53. The heaviest of the stable halogens, it exists at standard conditions as a semi-lustrous, non-metallic solid that melts to form a deep violet liquid at 114 °C (237 °F), and boils to a violet gas at 184 °C (363 °F). The element was discovered by the French chemist Bernard Courtois in 1811 and was named two years later by Joseph Louis Gay-Lussac, after the Ancient Greek Ιώδης 'violet-coloured'.
Titration is a common laboratory method of quantitative chemical analysis to determine the concentration of an identified analyte. A reagent, termed the titrant or titrator, is prepared as a standard solution of known concentration and volume. The titrant reacts with a solution of analyte to determine the analyte's concentration. The volume of titrant that reacted with the analyte is termed the titration volume.
Benedict's reagent is a chemical reagent and complex mixture of sodium carbonate, sodium citrate, and copper(II) sulfate pentahydrate. It is often used in place of Fehling's solution to detect the presence of reducing sugars. The presence of other reducing substances also gives a positive result. Such tests that use this reagent are called the Benedict's tests. A positive test with Benedict's reagent is shown by a color change from clear blue to brick-red with a precipitate.
Iodoform is the organoiodine compound with the chemical formula CHI3. It is a pale yellow, crystalline, volatile substance, with a penetrating and distinctive odor and, analogous to chloroform, sweetish taste. It is occasionally used as a disinfectant.
Potassium tetraiodomercurate(II) is an inorganic compound with the chemical formula K2[HgI4]. It consists of potassium cations and tetraiodomercurate(II) anions. It is the active agent in Nessler's reagent, used for detection of ammonia.
Gravimetric analysis describes a set of methods used in analytical chemistry for the quantitative determination of an analyte based on its mass. The principle of this type of analysis is that once an ion's mass has been determined as a unique compound, that known measurement can then be used to determine the same analyte's mass in a mixture, as long as the relative quantities of the other constituents are known.
Cerium(IV) sulfate, also called ceric sulfate, is an inorganic compound. It exists as the anhydrous salt Ce(SO4)2 as well as a few hydrated forms: Ce(SO4)2(H2O)x, with x equal to 4, 8, or 12. These salts are yellow to yellow/orange solids that are moderately soluble in water and dilute acids. Its neutral solutions slowly decompose, depositing the light yellow oxide CeO2. Solutions of ceric sulfate have a strong yellow color. The tetrahydrate loses water when heated to 180-200 °C.
Potassium dichromate, K2Cr2O7, is a common inorganic chemical reagent, most commonly used as an oxidizing agent in various laboratory and industrial applications. As with all hexavalent chromium compounds, it is acutely and chronically harmful to health. It is a crystalline ionic solid with a very bright, red-orange color. The salt is popular in laboratories because it is not deliquescent, in contrast to the more industrially relevant salt sodium dichromate.
Classical qualitative inorganic analysis is a method of analytical chemistry which seeks to find the elemental composition of inorganic compounds. It is mainly focused on detecting ions in an aqueous solution, therefore materials in other forms may need to be brought to this state before using standard methods. The solution is then treated with various reagents to test for reactions characteristic of certain ions, which may cause color change, precipitation and other visible changes.
Iodometry, known as iodometric titration, is a method of volumetric chemical analysis, a redox titration where the appearance or disappearance of elementary iodine indicates the end point.
The iodine clock reaction is a classical chemical clock demonstration experiment to display chemical kinetics in action; it was discovered by Hans Heinrich Landolt in 1886. The iodine clock reaction exists in several variations, which each involve iodine species and redox reagents in the presence of starch. Two colourless solutions are mixed and at first there is no visible reaction. After a short time delay, the liquid suddenly turns to a shade of dark blue due to the formation of a triiodide–starch complex. In some variations, the solution will repeatedly cycle from colorless to blue and back to colorless, until the reagents are depleted.
Ammonium acetate, also known as spirit of Mindererus in aqueous solution, is a chemical compound with the formula NH4CH3CO2. It is a white, hygroscopic solid and can be derived from the reaction of ammonia and acetic acid. It is available commercially.
Chloroplatinic acid (also known as hexachloroplatinic acid) is an inorganic compound with the formula [H3O]2[PtCl6](H2O)x (0 ≤ x ≤ 6). A red solid, it is an important commercial source of platinum, usually as an aqueous solution. Although often written in shorthand as H2PtCl6, it is the hydronium (H3O+) salt of the hexachloroplatinate anion (PtCl2−
6). Hexachloroplatinic acid is highly hygroscopic.
Bismuth(III) iodide is the inorganic compound with the formula BiI3. This gray-black salt is the product of the reaction of bismuth and iodine, which once was of interest in qualitative inorganic analysis.
Johann Georg Noel Dragendorff was a German pharmacist and chemist born in Rostock.
Mayer's reagent is an alkaloidal precipitating reagent used for the detection of alkaloids in natural products. Mayer's reagent is freshly prepared by dissolving a mixture of mercuric chloride and of potassium iodide in water. Most alkaloids are precipitated from neutral or slightly acidic solution by Mayer's reagent to give a cream coloured precipitate. This test was invented by the German Chemist, Julius Robert Von Mayer (1814–1878).
Bismuth oxynitrate is the name applied to a number of compounds that contain Bi3+, nitrate ions and oxide ions and which can be considered as compounds formed from Bi2O3, N2O5 and H2O. Other names for bismuth oxynitrate include bismuth subnitrate and bismuthyl nitrate. In older texts bismuth oxynitrate is often simply described as BiONO3 or basic bismuth nitrate. Bismuth oxynitrate was once called magisterium bismuti or bismutum subnitricum, and was used as a white pigment, in beauty care, and as a gentle disinfectant for internal and external use. It is also used to form Dragendorff's reagent, which is used as a TLC stain.
The murexide test is an analytical technique to identify the presence of caffeine and other purine derivatives in a sample. These compounds do not respond to the common alkaloid identification tests such as Dragendorff's reagent. In this test, crude drugs are mixed with a tiny amount of potassium chlorate and a drop of hydrochloric acid. The sample is then evaporated to dryness and the resulting residue is exposed to ammonia vapour. Purine alkaloids produce a pinkish-purple color in this test due to formation of murexide, which the test is named after.
Golden rain demonstration is made by combining two colorless solutions, potassium iodide solution and Lead(II) nitrate solution at room temperature to form yellow precipitate. During the chemical reaction, golden particles gently drop from the top of Erlenmeyer flask to the bottom, similar to watching the rain through a window. The golden rain chemical reaction demonstrates the formation of a solid precipitate. The golden rain experiment involves two soluble ionic compounds, potassium iodide (KI) and lead(II) nitrate (Pb(NO3)2). They are initially dissolved in separate water solutions, which are each colorless. When mixed, as the lead from one solution and the iodide from the other combine to form lead(II) iodide (PbI2), which is insoluble at low temperature and has a bright golden-yellow color. Although this is a reaction solely of the dissociated ions in solution, it is sometimes referred to as a double displacement reaction:
Bismuthyl — inorganic oxygen-containing singly charged ion with the chemical formula BiO+, is an oxycation of bismuth in the +3 oxidation state. Most often it is formed during the hydrolysis of trivalent bismuth salts, primarily nitrate, chloride and other halides. In chemical compounds, bismuthyl plays the role of a monovalent cation.
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