Qualitative Organic Analysis Lab Discussion
Qualitative Organic Analysis Lab Discussion
Exp. 7 Pre-Lab / Qualitative Organic Analysis Name:_________________________________ Score:______/ 10 1. Draw reaction schemes for: a) The reaction of acetone (2-propanone) with semicarbazide hydrochloride to form the semicarbazones. b) The reaction of acetone (2-propanone) with 2,4-dinitrophenylhydrazine to form the hydrazone. 2. Draw the mechanism for either reaction 1a or 1b (above). (Hint: See imine formation in the text.) 3. Explain the purpose and means of interpretation of the following tests: a) Beilstein b) Combustion c) Tollens d) Semicarbazone and / or 2,4 Dinitrophenylhydrazine 4. Your unknown is believed to be a ketone since it did not produce a silver mirror during the Tollens Test. You found the boiling point to be 1700C and so you suspect your compound is either 2,6-dimethyl-4heptanone or 2-octanone. Which derivative would you make to determine the identity of your unknown ketone, semi-carbazone or 2,4-dinitrophenyl hydrazine. (Refer to the table on pg. 35 of your manual to answer this question). 39 QUALITATIVE ORGANIC ANALYSIS Experiment 7 Introduction In this experiment, you will be issued an unknown aldehyde or ketone and asked to identify through spectroscopic it first through physical and chemical methods (Part l) and then as to the identity of methods (Part 2). A table of possible unknowns is provided. A claiminstructor before any the compound based on chemical methods must be submitted to your spectroscopic methods may be employed. Methods Part 1 —The Identification of an Unknown by Physical and Chemical when handling any Wear safety glasses during the entire laboratory period and use gloves performed in the chemicals. All chemicals, reactions and procedures should be used or unless otherwise hood. All organic wastes should be put in the hazardous waste bottle stated. such as color, 1) Preliminary Classification —Physical characteristics of the unknown have odor, physical state and crystalline form should be noted. Many compounds structure. crystal specific a characteristic colors or odors, or they crystallize with Compounds with a high degree of conjugation are frequently yellow to red. Amines have a often have a fishlike odor. Esters have a pleasant fruity or floral odor. Acids vapors corrosive have compounds sharp and pungent odor. As a note of caution, some and should be sniffed with the greatest of caution. 2) Melting Point or Boiling Point Determination —The melting point or the boiling point of an unknown compoundcan be extremelyuseful since it will drastically limit the compounds that are possible. Consequently,it is very important that these values are determined as carefully as possible. Refer to your laboratory text for proper techniques. If the melting point of a solid has a wide range (> 4-50C), it should be recrystallized. If the boiling point determination yielded a wide range or if the temperature did not hold constant during the determination,it should be redistilled and a new temperature range determined. Allowances should be made for errors as large as ±50C. p 40 3) Flame Tests -Qualitative Organic Analysis Lab Discussion
The Beilstein test and the Combustion test can be performed easily and quickly, and they often give valuable infomation. Notify your instructor before using any flames in the organic laboratory!!!!!! a) The Beilstein Test —A test for halides. Bend a small loop in the end of a short g g n copper wire. Heat the loop end of the wire in a Bunsen burner flame. After cooling, dip the wire directly into a small sample of the unknown. Now, heat the wire in the Bunsen burner flame again. The compound will first burn. After the burning, a green flame will be produced if a halogen is present. For comparison,it may be useful to run the test on a sample known not to contain a halogen and on a sample known to contain a halogen. b) The Combustion Test —A test for aromaticity. Place a small amount of the compound on a spatula and place it in the flame of a Bunsen burner. Observe whether a sooty flame is the result. Compounds giving a sooty yellow flame have a high degree of unsaturation and may be aromatic. For comparison,it may be useful to run the test on a sample that is not conjugated as well as on a sample that does contain conjugation. 4) Classification Test —differentiation between aldehydes and ketones. Most aldehydes and ketones give crystalline solids when reacted with 2,4-dinitrophenylhydrazine or semicarbazide as demonstrated during the preparation of derivatives section that follows. However, only aldehydeswill reduce chromium(VI)or silver(l). By these differences, you can distinguish between aldehydes and ketones. Both tests should be performed in case one is inconclusive. Tollens Test—The Tollens reagent must be prepared immediately before use. Note: Silver Nitrate is a skin irritant and can stain the skin. Wear gloves! To prepare the reagent, mix I mL of solution A (describedbelow) with I mL of solution B (described below) in a small beaker. A precipitate of silver oxide will form. To complete the Tollens reagent, add 2 mL of ammonia (NH40H) solution to dissolve the silver oxide (This is now the Tollens reagent). In a separate container dissolve 4 drops of liquid unkown or 40 mg (approximate) of solid unkown in 2 mL ofbis(2ethoxyethyl) ether. Add this solution, a little at a time, to a small Erlenmeyer flask containing 2-3 mL of Tollens reagent.Qualitative Organic Analysis Lab Discussion
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Stir the mixture and warm gently on a hot plate for about 5-10 minutes. If a mirror of silver is deposited on the inner walls of the Erlenmeyer, the test is positive. Most aldehydes reduce ammoniacal silver nitrate solution to give a precipitate of silver metal. RCHO + 2Ag + RCOONl-14 + 1-120+ NH3 Solution A: Dissolve 0.3 g of silver nitrate in 3 mL of water. Solution B: Prepare a 10% sodium hydroxide solution. 41 of correct identification the of tests 5) Preparation of Derivatives—One of the principal compound by a chemical the convert to derivative. an unknown compound comes in trying compound is called a reaction to another known compound. This second very similar compounds. The derivative is a way of distinguishing two otherwise2,4-DNP) based on your Select the best derivative to make (semicarbazoneor provided in the derivatives as suspicions of unknown identity and the melting points of following tables. you see fit) Dissolve a) Semnicarbazones—(you can adjust the scale of this reaction as acetate in 1.3 mL of 0.25 g of semicarbazide hydrochloride and 0.38 g of sodium Mix the two water. Then dissolve 0.25 g of the unknown in 2.5 mL of ethanol. for mixture solutionstogetherin a 25 mL Erlenmeyerflask and gently heat the heat. After about five minutes. If the solutionbegins to boil, remove it from scratch formed, heating, place the reaction flask in a beaker of ice. If not solid has derivative. the sides of the flask with a glass rod to induce crystallization of the Collect the derivativeby vacuumfiltration. If necessaryit can be recrystallized from ethanol. b) 2,4-Dintrophenylhydrazones(2,4-DNP)- (you can adjust the scale of this reaction as you see fit) Dissolve 1.5 g of 2,4-dinitrophenylhydrazinein 7.5 mL of concentratedsulfuric acid. In a beaker mix 10 mL of water and 35 mL of 95% ethanol. With vigorous stirring, slowly add the 2,4-dinitrophenylhydrazine solution to the aqueous ethanol mixture.Qualitative Organic Analysis Lab Discussion
If solid remains after thorough mixing, filter the 2,4-DNP solution by vacuum filtration with a Hirsch funnel. Place 10 mL of the 2,4-DNP solution in a test tube and add an estimated 1 mmol of the unknown compound. If the unknown is a solid, it should be dissolved in a minimum amount of 95% ethanol or 1,2-dimethoxyethanebefore it is added. If crystallization is not immediate, gently warm the solution on a hot plate and then set it aside to crystallize. Collect the product by vacuum filtration. 6) Other tests may include the determinationof density, refractive index and solubility. 7) Conclusions from Physical and Chemical Methods —Considering all of the data, make a conclusion as to the identity of your known sample. After submitting your answer to your instructor, you may request a genuine sample of the compound for comparison. You may perform any of the physical and chemical methods of analysis on the genuine sample that would be useful. However, you should consider trying mixed melting point for solids and IR and/or mixed gas chromatography for liquids. 42 Part 2 —The Identification of an Unl€n0″T1by Spcctroqcopic Methods Spectroscopic data is to bc acquircd and analyzcd in ordcr to confirm or rcfutc your conclusions in Part 1. Use all spectroscopicdata to dctcrminc thc corrcct idcntity. The g g methods available are infrared spectroscopy (IR), nuclcar magnctic rcsonancc (NMR) and gas chromatography in tandcl)l with numssspcctromctry(GC/MS). You must assign all spectral features OOIat docs “assign” mcan?) and submit the data with your report along “ith any literature data that you discussed or used for comparison. Qualitative Organic Analysis Lab Discussion
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