WWW.SA.I-PDF.INFO
FREE ELECTRONIC LIBRARY - Abstracts, books, theses
 
<< HOME
CONTACTS



Pages:     | 1 || 3 |

«Identifying an Unknown Compound by Solubility, Functional Group Tests and Spectral Analysis This handout is a supplement to Signature Lab Series ANAL 0727 ...»

-- [ Page 2 ] --

Classification tests are based on the chemical reactivity characteristic of particular functional groups. The results are intended to be visual and obvious, such as a color change, formation of a precipitate, or evolution of bubbles. Sometimes the results are difficult to interpret or are borderline between positive and negative.

There are two inviolable rules when performing classification tests. First, perform the test exactly as described. If the procedure says add 3 drops, do not add 4 or 5. Second, always perform tests in duplicate. Perform the test on a known compound that will result in a positive test (known positive);

perform the test on a known compound that will result in a negative test (known negative); and perform the test on the unknown compound. This direct visual comparison of the results of testing the unknown against a known positive test and a known negative test confirms that the reagents are good and you are performing the test properly.

No classification test is always accurate in every case. A compound may produce a false positive if the test is positive even though the compound giving the test is not of the expected type. For example, some phenols give a positive test for aldehydes. A false negative occurs if the test is negative even though the compound undergoing the test is the expected type. For example, less reactive aldehydes or very insoluble aldehydes may fail to give a positive test for aldehydes.

The following classification tests are performed in this experiment and are among those tests commonly performed in qualitative organic analysis.

Bromine in Cyclohexane

Alkenes react with bromine (Br2) in cyclohexane, an orange solution, to produce colorless vicinal dibromides, as shown in Equation 5. This test is commonly used for water-insoluble compounds.

Alkenes with strong electron-withdrawing groups may fail to react. Phenols, phenyl ethers, and some aldehydes and ketones also react to decolorize bromine in cyclohexane.

–  –  –

Alkenes are oxidized to diols by dilute potassium permanganate (KMnO4), as shown in Equation 6. The purple color of KMnO4 disappears and is replaced by the brown color of manganese dioxide (MnO2).

Because KMnO4 is a strong oxidizing agent, aldehydes, some primary and secondary alcohols, phenols, and aromatic amines can also react.

–  –  –

Alkyl halides react with silver nitrate (AgNO3) in ethanol by the SN1 mechanism. Tertiary, allylic, and benzylic halides give an immediate precipitate at room temperature, as shown in Equation 7. Secondary halides require several minutes to give a precipitate, primary halides require hours.

–  –  –

Sodium Iodine in Acetone A saturated solution of sodium iodide (NaI) in acetone reacts rapidly with primary, allylic, and benzylic chlorides or bromides by the SN2 mechanism. Secondary halides react slowly, while tertiary halides are unreactive. The corresponding alkyl iodides and a precipitate of sodium chloride or sodium bromide result, as shown in Equation 8.

–  –  –

TCICA Test In acid solution, 1,3,5-trichloroisocyanuric acid (TCICA) slowly releases chlorine, which is an oxidizing agent. The reaction is rapid in the presence of an oxidizable compound such as a primary of secondary alcohol, as shown in Equation 9. The produce is isocyanuric acid, which is very soluble in water but precipitates from the solvent acetonitrile. The time it takes for isocyanuric acid precipitate to appear is characteristic of the type of alcohol. Secondary alcohols react fastest, within 15-30 seconds; primary alcohols produce a precipitate usually within 3-7 minutes, although some can take up to 20 minutes;

tertiary alcohols are not oxidizable at room temperature and produce no precipitate within an hour.

–  –  –

Iron(III) Chloride Many phenols react with iron(III) chloride (FeCl3) solution to give brightly colored complexes. Many of these complexes are short-lived; the color may fade soon after it forms. Some phenols may not react at all, so a negative iron(III) chloride test is inconclusive. Aldehydes or ketones with significant enolic character can also give colored complexes with FeCl3.

Bromine in Water

–  –  –

2,4-Dinitrophenylhydrazine Aldehydes and ketones rapidly form yellow, orange, or red precipitates with 2,4-dinitrophenylhydrazine (DNP) reagent, as shown in Equation 11.

–  –  –

Schiff Test In a complex series of reactions that is not completely understood, Schiff reagent reacts only with aldehydes to produce a purple fuchia solution. A faint pink color results from the initial reaction and does not constitute a positive test. The Schiff test is the most sensitive rest for aldehydes. However, the Schiff test is subject to giving false positives and false negatives.

Table 2 Known Positive And Negative Test For Functional Group Classification Tests

–  –  –

Based on the data you collected in Week 1 of the lab, you should have decided which • experiments you need to conduct to distinguish the functional groups present in your unknown compound.

In this experiment, you will identify two unknowns by functional groups using solubility tests and • classification tests. Table 2 list known positive and known negative compounds for classification tests.





Note: You should not run all of the experiments listed below on each unknown sample. You must • use the solubility data from Week 1 to decided which tests are nessary for your compounds.

Equipment

–  –  –

Procedure Week 2. Performing the Bromine in Cyclohexane Test for Alkenes CAUTION—Bromine  (Br2)  is  toxic  and  oxidizing.    It  causes  severe  burns.    Always  use  a  fume  hood   when  working  with  Br2.    Acetone  and  cyclohexane  are  flammable  and  irritating.    Keep  away  from   flames  or  other  heat  sources.   Place 1 mL of cyclohexane in a small test tube. Add 3 drops of Br2/H2O. Mix until the bromine color appears in the top cyclohexane layer.

For liquid samples, add 2 drops of sample to the Br2/H2O. Tap the tube with your finger to mix or stir gently with a glass stirring rod. Note and record whether or not the orange color disappears.

For solid samples, place 30 mg of solid into a test tube. Add 5 drops of acetone. Add the acetone solution to the Br2/H2O. Tap the tube with your finger to mix or stir gently with a glass stirring rod. Note and record whether or not the orange color disappears.

If the orange color disappears quickly, the sample may be an alkene.

NOTE: Phenols, phenyl ethers, and some aldehydes and ketones may test positive.

Performing the Potassium Permanganate Test for Alkenes CAUTION—1%  Potassium  permanganate  (KMnO4)  is  corrosive  and  oxidizing.   If your sample is water-soluble, place 1-2 mL of water into a small test tube. If your sample is waterinsoluble, place 1-2 mL of 95% ethanol into a small test tube.

Add 2 drops of a liquid sample or about 30 mg of a solid sample. Add 2 drops of 1% KMnO4.

Tap the tube with your finger to mix or stir gently with a glass stirring rod. Let the mixture stand 10-20 s.

Note and record whether or not the purple color disappears.

If the purple color disappears and a brown color or precipitate appears, the compound may be an alkene.

Note: The brown color or precipitate may not appear. Aldehydes, some primary and secondary alcohols, phenols, and aromatic amines may test positive.

Performing the Silver Nitrate in Ethanol Test for 2° and 3° Alkyl Halides

CAUTION—Silver  nitrate  (AgNO3)  in  ethanol  is  flammable,  toxic,  and  oxidizing.    It  also  stains  the   skin.    Keep  away  from  flames  or  other  heat  sources.   Place 1 mL of 2% AgNO3 in ethanol into a small test tube.

For liquid samples, add 2 drops of sample to the 2% AgNO3. Tap the tube with your finger to mix or stir gently with a glass stirring rod.

For solid samples, place 30 mg of solid into a test tube. Add 5 drops of ethanol. Add this ethanol solution to the 2% AgNO3 in ethanol. Tap the tube with your finger to mix or stir gently with a glass stirring rod. Note and record whether or not a precipitate forms.

An immediate precipitate indicates a tertiary, allylic, or benzylic halide.

Performing the Sodium Iodide in Acetone Test for 1° and 2° Alkyl Halides CAUTION—Sodium  iodide  (NaI)  in  acetone  is  flammable  and  irritating.    Keep  away  from  flames  or   other  heat  sources.   Place exactly 1.0 mL of NaI in acetone into a small test tube. Add 3 drops of a liquid sample. Tap the tube with your finger to mix or stir gently with a glass stirring rod. Allow the tube to stand 3-6 min at room temperature. Note and record whether or not a precipitate forms.

A white precipitate indicates a primary, allylic, or benzylic halide.

Performing the TCICA Test for Alcohols

CAUTION—1,2,5 ­trichloroisocyanuric  acid  (TCICA)  is  corrosive  and  oxidizing.    Acetonitrile  is  toxic.     5%  Hydrochloric  acid  (HCl)  is  toxic  and  corrosive.   Place 0.5 mL of the TCICA test solution into a small test tube. Add 1 drop of 5% HCl. Tap the tube with your finger to mix or stir gently with a glass stirring rod.

For liquid samples, add 1 drop of the sample. Tap the tube with your finger to mix or stir gently with a glass stirring rod.

For solid samples, dissolve about 20 mg of solid in 1-2 drops of acetonitrile. Add this solution to the TCICA/HCl solution.

Note and record whether or not a precipitate forms.

The formation of a precipitate within one min indicates a secondary alcohol; the formation of a precipitate between 3-20 min indicates a primary alcohol.

Performing the Iron(III) Chloride Test for Phenols CAUTION—Iron(III)  chloride  (FeCl3)  is  toxic  and  corrosive.    Ethanol  is  flammable  and  toxic.    Keep   away  from  flames  or  other  heat  sources.   Place 1 mL of 95% ethanol into a small test tube. Add 2 drops of a liquid sample or about 30 mg of a solid. Add 3-5 drops of 3% FeCl3. Tap the tube with your finger to mix or stir gently with a glass stirring rod. Note and record any formation of a brightly colored solution.

The presence of bright color, even briefly, indicates a phenol.

NOTE: Some aldehydes or ketones also give colored complexes with FeCl3.

Performing the Bromine in Water Test for Phenols CAUTION—Bromine  (Br2)  is  toxic  and  oxidizing.    It  causes  severe  burns.    Always  use  a  fume  hood   when  working  with  Br2.    Ethanol  is  flammable.    Keep  away  from  flames  or  other  heat  sources.   Place 1 mL of 95% ethanol into a small test tube. Add 5 drops of a liquid sample or about 30 mg of a solid.

Add a drop of water. Tap the tube with your finger to mix or stir gently with a glass stirring rod.

Add 1 drop of Br2/H2O. Tap the tube with your finger to mix or stir gently with a glass stirring rod.

Note and record whether or not the orange color disappears.

The disappearance of the orange color indicates a phenol.

Performing the 2,4-DNP Test for Aldehydes and Ketones CAUTION—2,4 ­Dinitrophenylhydrazine  (2,4 ­DNP)  solution  is  corrosive  and  irritating.    It  stains  skin   and  clothing.   For liquid samples, place 1 drop of sample into a clean, dry test tube. Add up to 20 drops of 2,4-DNP solution. Tap the tube with your finger to mix or stir gently with a glass stirring rod.

For solid samples, add about 30 mg of solid into a clean, dry test tube. Add 0.5 mL of ethanol. Tap the tube with your finger to mix or stir gently with a glass stirring rod. If the unknown does not dissolve, prepare a warm-water bath by placing 175-200 mL of tap water into a 250-mL beaker. Use a hot plate to heat the water to 40°C. Place the test tube into a warm-water bath and swirl the tube until the unknown is dissolved. Cool the solution to room temperature. Add up to 20 drops of 2,4-DNP solution. Tap the tube with your finger to mix or stir gently with a glass stirring rod.

Note and record whether or not a precipitate forms.

An immediate, brightly colored precipitate indicates an aldehyde or ketone.

Preforming the Schiff Test for Aldehydes.

CAUTION – Schiff solution contains pararosaniline hydrochloride, sodium hydrogen sulfite, and HCl. Schiff solution is toxic, irritation and a suspected carcinogen.

Add 1 drop of a liquid sample or about 15 mg of a solid sample a clean, dry test tube. Place 2 mL of Schiff solution in a test tube. Mix well. After 5 min, mote the color of the solution and record your observation.

A fuchsia color indicates an aldehyde.

Cleaning Up And Getting the Spectra Once you believe you have identified the functional groups present in your unknown, check with your TA to see if you have determined them correctly.

After your TA has confirmed your assignment, you should clean-up your work area and rinse any remaining unknown compound into the organic waste using acetone. DO NOT PUT YOUR UNKNOWN INTO THE WASTE UNTIL YOU HAVE CLEARED IT WITH YOUR TA. If you have misassigned your functional groups and disposed of your unknown, you will be penialized to obtain an additional sample.

Thoroughly rise the vials you unknowns came in, and them present them to your TA for inspection. Once your TA is satisfied that you have cleaned-up properly, they will give you the spectra so you can complete Part 3 of the lab.

Wash your hands with soap or detergent before leaving the laboratory.

–  –  –

In Parts A and B, you used solubility and chemical reactivity test to identify the functional group(s) contained within your unknown compound. Using these results in conjunction with molecular formula and the spectra data that you have received, please fully identify the unknown compound. Assign the H and C NMR spectra completely.

In your lab report, please state the identity of each of your unknown compounds along with the unknown number. Discuss the relevance of the solubility and chemical tests to this structural assignment.

Pre-Laboratory Assignment

1. What risks do you run by not performing the qualitative tests in duplicate?

2. (a) Why is it important to have clean test tubes before running a test?

(b) Before which tests should acetone not be used to clean the test tubes?

3. Why is water solubility the first test to run?

4. Why run solubility tests before running the functional group classification tests?

5. Determine the functional group present in these unknown:

(a) Unknown A is soluble in water and gives bubbles with5% NaHCO3.

(b) Unknown B is insoluble in water, insoluble in 5% NaOH, but soluble in 5% HCl.

(c) Unknown C is insoluble in water, insoluble in 5% NaOH, insoluble in 5% HCl, soluble with a color change in conc. H2SO4, and decolorizes both KMnO4 (aq) and bromine in cyclohexane.

(d) Unknown D is soluble in water, does not produce bubbles with 5% NaHCO3, gives a precipitate with 2,4-DNP, and gives a fuchsia color with the Schiff test.

6. In each of the following cases, describe the next test you would perform.

(a) Unknown X is insoluble in water, 5% NaOH, 5% HCl, and conc. H2SO4.

(b) Unknown Y is insoluble in water, soluble in 5% NaOH, and insoluble in 5% NaHCO3.

(c) Unknown Z is insoluble in water, insoluble in 5% NaOH, insoluble in 5% HCl, and soluble in conc. H2SO4.

7. If your unknown is soluble in water and does not produce bubbles with 5% NaHCO3, what steps would you follow to determine if your unknown is an amine?

Post-Laboratory Questions

1. Record the solubility results for each unknown that you tested. Describe your observations and briefly explain your conclusions.

2. Record the results of the classification tests that you conducted for each unknown you tested.



Pages:     | 1 || 3 |


Similar works:

«WWF HQ: 'Stringent is an understatement' | Magazine Features | Building 01/11/2013 17:41 Friday01 November 2013 WWF HQ: 'Stringent is an understatement' 31 October 2013 | By Thomas Lane At the World Wildlife Fund’s new HQ in Surrey, Willmott Dixon has taken sustainable construction to new levels of rigour, forensically tracking the carbon content of every single element, and even building an FSC-certified workshop on site. So has the result been worth it? If you happened to be a leading...»

«SECTION 5. TETHER DATA 5.1 General This handbook would not be complete without providing the user with specific data and other information relevant to the analysis of tether applications. To the authors' knowledge, the best summarization of this data is contained in J. A. Carroll's Guidebook for Analysis of Tether Applications, published in 1985 under contract to the Martin Marietta Corporation. It provides a concise review of those technical areas which are essential to tether analyses. For...»

«SMT 300 Smoke Machine Tester Operator Manual with UltraTraceUV® Dye Solution F00E900291 ii | Contents | SMT 300 Operator Manual Contents TO PREVENT PERSONAL INJURY AND/OR DAMAGE TO VEHICLE OR EQUIPMENT • Use this equipment in the manner specified by the 1 Introduction manufacturer. • Understand operating procedures / follow all safety 1 SMT 300 Technical Specifications precautions. • Correctly connect SMT 300 tester to battery and chassis ground. 2 Items Included with the SMT 300...»

«International Professional Groomers, Inc CERTIFICATION GUIDELINES INTERNATIONAL PROFESSIONAL GROOMERS, INC. T he International Professional Groomers, Inc is an association which certifies Professional Pet Groomers all over the world, providing International industry standards, a Code of Ethics and extensive examination process, certifying groomers at two levels. The IPG globally promotes and preserves the professional certifications and accreditations of Pet Groomers, Grooming Salons, and...»

«A Framework for the Automatic Calculation of Quality of Experience in Telematic Services A. Sánchez-Macián1, D. López1, J. E. López de Vergara2, E. Pastor1 Dpto. de Ingeniería Telemática Dpto. de Ingeniería Informática Universidad Politécnica de Madrid Universidad Autónoma de Madrid Ciudad Universitaria, S/N Ciudad Universitaria de Cantoblanco Madrid, Spain Madrid, Spain {aasmp,lopezber,encarna}@dit.upm.es jorge.lopez_vergara@uam.es Abstract This paper presents a framework based on...»

«Research Report Agreement T4118, Task 04 Unmanned Aerial Vehicles The Use of Small Unmanned Aircraft by the Washington State Department of Transportation by Edward D. McCormack Senior Research Engineer Washington State Transportation Center (TRAC) University of Washington, Box 354802 1107 NE 45th Street, Suite 535 Seattle, Washington 98105-4631 Washington State Department of Transportation Technical Monitor Ted Trepanier, State Traffic Engineer Prepared for Washington State Transportation...»

«UNDERSTANDING CLAY RECOGNITION AND PROCESSING by Miska Petersham Technical Reviewers: Daniel Rhodes Gerald Rowan Published by: Volunteers in Technical Assistance (VITA) 1815 North Lynn Street, Suite 200 Arlington, Virginia 22209 USA Telephone 703/276-1800 Cable VITAINC Telex 440192 VITAUI PR EFACE This paper is one of series published by Volunteers in Techni­ a cal Assistance to provide an introduction to specific state-of­ the-art technologies of interest to people in developing coun­...»

«© Copyright, Princeton University Press. No part of this book may be distributed, posted, or reproduced in any form by digital or mechanical means without prior written permission of the publisher. CHAPTER 1 A TIME OF DYING If you could travel back in time 260 million years, you would find our planet had an unfamiliar geography. Nearly all of the landmasses were united into a single, giant continent. This was Pangea, and it stretched from pole to pole. On the other side of the world you would...»

«The Gravitational Million-Body Problem Douglas Heggie Department of Mathematics and Statistics University of Edinburgh, Edinburgh EH9 3JZ, Scotland Piet Hut School of Natural Sciences Institute for Advanced Study, Princeton, NJ 08540, U.S.A. For Eiko, Linda, Caroline and Alison Table of Contents Preface iii PART I INTRODUCTIONS 1 1 Astrophysics Introduction 3 2 Theoretical Physics Introduction 15 3 Computational Physics Introduction 25 4 Mathematical Introduction 35 THE CONTINUUM LIMIT: N →...»

«TOC TotalRecallPress.com This Book is Sponsored by TotalRecall Publications, Inc. 1103 Middlecreek Friendswood, Texas 77546 281-992-3131 281-482-5390 Fax Copyright © 2007 by: Sri Sathya Sai Veda Pratishtan Secunderabad, India (A Charitable Trust) All rights reserved. Printed in the United States of America. Except as permitted under the United States Copyright Act of 1976, No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means...»

«榮昌科技股份有限公司 GRAND-TEK TECHNOLOGY CO.,LTD. 文件名稱:榮昌科技 HSF 技朮標準 文件編號:03-133 文件版次:F Doc.: Grand-Tek Technology HSF Technical Standard Doc.No. : 03-133 Doc. Rev: F 榮昌科技 HSF 技朮標準 Grand Tek Technology HSF Technical Standard 文件編號:03-133 Doc. No.: 03-133 制訂部門:工程部 Issued Department: Engineering Department 制訂日期:2008 年 08 月 01 日 Issued Date: August 01, 2008 生效日期﹕2013 年 06...»

«Into the Breach: The Case for Robust Noncapital Proportionality Review Under State Constitutions Samuel Weiss* INTRODUCTION The Eighth Amendment forbids cruel and unusual punishments.1 The Supreme Court has found in the Amendment a guarantee that punishment be proportionate to the crime.2 Although the requirement technically applies equally to all punishment, in practice the Court has used the guarantee strictly to regulate capital punishment — a practice it recently extended to life without...»





 
<<  HOME   |    CONTACTS
2017 www.sa.i-pdf.info - Abstracts, books, theses

Materials of this site are available for review, all rights belong to their respective owners.
If you do not agree with the fact that your material is placed on this site, please, email us, we will within 1-2 business days delete him.