DETERMINATION OF FUNCTIONAL GROUPS

ELEMENTAL ANALYSIS AND DETERMINATION OF FUNCTIONAL GROUPS: 

ELEMENTAL ANALYSIS AND DETERMINATION OF FUNCTIONAL GROUPS Facilitated by, Dr.Sangamesh B Puranik Professor Presented by, Masood Mohammad, Dept. of pharmaceutical analysis,

Elemental analysis : 

Elemental analysis Elemental Analysis is a process where a sample of a compound is analyzed to determine its elemental composition. Elemental analysis can be qualitative (determining what elements are present), and it can be quantitative (determining how much of each are present). Elemental analysis falls within the ambit of analytical chemistry

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For organic chemists, elemental analysis or "EA" almost always refers to CHNX analysis—the determination of the mass fractions of carbon, hydrogen, nitrogen, and heteroatoms (X) (halogens, sulfur ) of a sample. This information is important to help determine the structure of an unknown compound, as well as to help ascertain the structure and purity of a synthesized compound.

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1 Methods 1.1 Quantitative 1.2 Qualitative

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Methods The most common form of elemental analysis, CHN analysis , is accomplished by combustion analysis . In this technique, a sample is burned in an excess of oxygen, and various traps collect the combustion products—carbon dioxide, water, and nitric oxide. The masses of these combustion products can be used to calculate the composition of the unknown sample.

Quantitative : 

Quantitative Quantitative analysis is the determination of the mass of each element or compound present. Other quantitative methods include: Gravimetry , where the sample is dissolved and then the element of interest is precipitated and its mass measured or the element of interest is volatilized and the mass loss is measured. Optical atomic spectroscopy , such as flame atomic absorption, graphite furnace atomic absorption , and inductively coupled plasma atomic emission, which probe the outer electronic structure of atoms.

Qualitative : 

Qualitative To qualitatively determine which elements exist in a sample, the methods are: Mass spectrometric atomic spectroscopy , such as inductively coupled mass spectrometry, which probes the mass of atoms. Other spectroscopy which probes the inner electronic structure of atoms such as X-ray fluorescence , particle-induced X-ray emission , X-ray photoelectron spectroscopy , and Auger electron spectroscopy . Chemical methods Sodium fusion test Schöniger oxid ation

DETERMINATION OF NITRATES:: 

DETERMINATION OF NITRATES: PRINCIPLE: Nitrates are reduced to ammonia by means of aluminum, zinc in strongly alkaline solution. 3NO3 - + 8Al +5OH +2H2O →8AlO2+3NH3 The ammonia is distilled into excess of standard acid. Nitrates are similarly reduced, and must be allowed for if nitrate alone is to be determined.

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PROCEDURE: Weigh out accurately about 1.0g of the nitrate ↓ Dissolve it in water and transfer the solution quantitatively to the distillation flask. ↓ Dilute to about 240ml. Add 3g of pure, finely divided Devarda’s alloy Fit up the apparatus completely and place 75-100ml standard 0.2M hydrochloric acid ↓ Introduce 10ml of 20% (0.5M) sodium hydroxide solution through the funnel, and immediately close the trap. ↓ Warm gently for 1hr until the reduction of nitrate to ammonia is complete ↓

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Then boil the liquid gently and continue the distillation until 40-50 ml of liquid remains in the distillation flask. Open the tap before removing the flame. Wash the condenser with a little distilled water and titrate the contents of the receiver plus the washings with standard 0.2M sodium hydroxide, using methyl red as indicator. Perform the blank titration with distill water

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DETERMINATION OF AMINO GROUP There are four methods which can be employed for the estimation of amino group. They are as follows Acetylation method Bromination method Titration in aqueous or non aqueous media Determination of equivalent weight of amine by conversion to picrate and its titration in non aqueous media

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ACETYLATION METHODS: Generally amines undergo Acetylation reaction in presence of excess of acetic anhydride in pyridine at room temperature. The excess of acetic anhydride is decomposed with water and the acetic acid generated is determined by titration with standard solution of alkali. Simultaneously a blank determination is also performed. The difference between the two readings gives the quantity of acetylating agent consumed by amine

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RNH 2 + (CH 3 CO 2 )O → RNHCOCH 3 +CH 3 COOH R 2 NH + (CH 3 CO 2 )O → R 2 NCOCH 3 +CH 3 COOH In the reaction the amine is kept constant with acetylating agent for about 30 min at room temperature. In general double the quantity of acetylating agent is added than theoretically required. The experimental conditions may vary from one amine to another one. Some amines may require longer time for acetylation than others

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If substituent’s groups like nitro-methyl or halogen are present then amino group may performed at room temperature only. A large number of 1 0 and 2 0 aliphatic, aromatic and heterocyclic amines are determined by this method.

EXPERIMENTAL PROCEDURE: : 

EXPERIMENTAL PROCEDURE : Introduce a weighed sample containing about 2 milli equivalent of amine into a glass stoppered iodine flask and dissolve in 10 ml of pyridine. Add 10 ml of acetic anhdride pyridine reagent and stopper the flask. Set the flask aside for 30 min with occasional agitation. Add about 10 ml of water and mix the contents. Rinse the sides of the flask and stopper with 10 to 15 ml of n- butanol .

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Titrate the contents of the flask with standard alcoholic sodium hydroxide solution (0.5 N) using mixed indicator and note the reading of titrant (A). Following the same procedure simultaneously without sample (blank) perform titration and note the reading (B). % of amino group = (B-A) × 16.03 ×N × 100/ w × 1000 Where, B = volume of alkali required for blank A = volume of alkali required for sample N = normality of sodium hydroxide W = weight of sample in grams

DETERMINATION OF ALDEHYDES AND KETONES : 

DETERMINATION OF ALDEHYDES AND KETONES Both aldehydes and ketones contain the carbonyl group (c=o) therefore, both undergo a number of similar reactions. Although aldehydes and ketones resemble closely each other in structure and in their chemical reactions, they may be distinguished by the relative ease with which aldehydes are oxidised to acids. The silver mirror formed when an aldehyde is treated with ammonical silver nitrate is not characteristic of ketones

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This test has been widely used to distinguish between these two classes of compounds and to determine aldehydes in presence of ketones . aldehydes and ketones can be determined by using the following reagents: 2,4-dinitrophenyl hydrazine(for ketones ) Sodium bisulfate (for Aldehydes ) Hydroxylaminehydrochloride -pyridine(for Aldehydes & ketones )

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2,4-DINITROPHENYL HYDRAZINE : The reaction between carbonyl compounds and hydrazine has been employed for their analysis. It has been found that an excess of the hydrazine and higher than reflux temperatures may help in obtaining result, close to quantitative yields. The cause of the reaction can be measured by weighing the hydrazone produced. In general, the most widely used hydrazine is 2,4-dinitrophenyl hydrazine

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SODIUM BISULFITE: Aldehydes can be analysed by the reaction with Sodium bisulfite

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The above obtained bisulfite addition products are not determined gravimetrically. Instead, the quantity of bisulfite ion entering into the reaction is measured. In the reaction a measured excess of the bisulfite solution is employed and the excess reagent is determined by its reaction with an excess of iodine. NaHSO 3 + I 2 + H 2 O → NaHSO 4 + 2HI I 2 + 2Na 2 S 2 O 3 → 2NaI + Na 2 S 4 O 6

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HYDROXYLAMINE-PYRIDINE : Reaction of aldehydes or ketones with hydroxyl amine results in the formation of oximes . If proper conditions are present, the reaction will be quantitative. Although oximes are insoluble in dilute acids or in aqueous solutions, they are not usually quantitatively precipitated and therefore cannot determine gravimetrically. The reaction is determined by titration of the liberated HCL or by measuring the excess of hydroxylamine employed. The former is simpler and more frequently used. This method is employed for the assay of benzaldehyde in U.S.P.

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HCl + NaOH → NaCl + H 2 O In this titration, to locate the end point, the best indicator is bromophenol blue

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REFERENCES : G. Devala Rao , A Text Book of Pharmaceutical Analysis, Vol-1, 5 th edition, P.no : 84-95, Birla publication pvt . Ltd, delhi , 2010. G. Vidya sagar , Basics of Drug Analysis, p.no : 243-258, Pharmamed press publishers, Hyderabad, 2009. Vogel's - Textbook of quantitative chemical analysis, 5th Edition;Longmann scientific & Technicals , London, 1989. Skoog , DA, Holler, FJ, Crouch, SR. Principles of instrumental analysis. 6 th ed., Baba Barkha Nath printers, Haryana, 2007

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