11.1: Properties of Alcohol, Aldehydes and Ketones Lab Procedure
- Page ID
- 306790
\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)
\( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)
\( \newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\)
( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\)
\( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)
\( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\)
\( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\)
\( \newcommand{\Span}{\mathrm{span}}\)
\( \newcommand{\id}{\mathrm{id}}\)
\( \newcommand{\Span}{\mathrm{span}}\)
\( \newcommand{\kernel}{\mathrm{null}\,}\)
\( \newcommand{\range}{\mathrm{range}\,}\)
\( \newcommand{\RealPart}{\mathrm{Re}}\)
\( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)
\( \newcommand{\Argument}{\mathrm{Arg}}\)
\( \newcommand{\norm}[1]{\| #1 \|}\)
\( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\)
\( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\AA}{\unicode[.8,0]{x212B}}\)
\( \newcommand{\vectorA}[1]{\vec{#1}} % arrow\)
\( \newcommand{\vectorAt}[1]{\vec{\text{#1}}} % arrow\)
\( \newcommand{\vectorB}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)
\( \newcommand{\vectorC}[1]{\textbf{#1}} \)
\( \newcommand{\vectorD}[1]{\overrightarrow{#1}} \)
\( \newcommand{\vectorDt}[1]{\overrightarrow{\text{#1}}} \)
\( \newcommand{\vectE}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{\mathbf {#1}}}} \)
\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)
\( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)
\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Learning Objectives
- Study the chemical properties of alcohols, aldehydes and ketones.
- Perform solubility test in water, and organic solvents
- Test the reactivity with various chemical reagents.
Background
Structure of Alcohols
Alcohols are organic compounds containing a hydroxyl (R-OH) functional group bonded to a carbon atom that is not bonded to a carbonyl carbon (C=O). If the hydroxyl group is bonded to an aromatic ring (benzene ring), a class of compounds called phenols are form, which have properties different than regular alcohols, and will not be used in this experiment.
Alcohols can be separated into three subclasses, primary (1o ), secondary (2o ) and tertiary (3o ) based on the number of alkyl (R-) groups attached to the carbon atom with the hydroxyl (OH) group attached.
Physical Properties of Alcohols
The most common alcohols are colorless liquids at room temperature. Their melting and boiling points are considerably higher than those of alkanes, alkenes, and alkynes of similar size due to the ability to hydrogen bond. The ability to form hydrogen bonds also makes low molar mass alcohols soluble in water. However, as the alkane portion of the molecule increases in size the solubility decreases, because the hydrogen bonds formed by the alcohol group cannot counteract the nonpolar alkane part.
Chemical Properties of Alcohols
Chemically alcohols undergo two main categories of reactions: oxidation and dehydration. There are several common oxidizing agents (compounds that will oxidize organic molecules). These include:
- Potassium Permanganate
- Chromic Acid
- Tollens reagent
- Fehling’s/Benedict’s reagent
Due to the complex reaction mechanisms and balancing required, we will focus on the organic compounds formed in the reactions only. Depending on the classification of alcohol (primary, secondary, tertiary) they will be oxidized to different classes of molecules. The reaction results in the replacement of the OH group by either an Aldehyde, Carboxylic Acid or Ketone group.
\[ \text{Primary alcohol} \ce{->[\text{[O]}] Aldehyde + H2O ->[\text{[O]}] } \text{Carboxylic acid} \]
\[ \text{Secondary alcohol} \ce{->[\text{[O]}] Ketone + H2O ->[\text{[O]}] NR} \]
\[ \text{Tertiary alcohol} \ce{->[\text{[O]}] NR } \]
Structure of Aldehydes and Ketones
Aldehydes and Ketones are organic compounds containing a carbonyl carbon functional group. Carboxylic Acids and Esters also contain a carbonyl carbon, and will be explored in a future experiment. The carbonyl carbon is a polar group with the carbon having a slight excess of positive charge and the oxygen atom having a slight excess of negative charge.
Chemical Properties
Aldehydes and ketones are created by the mild oxidation of primary and secondary alcohols. One such method to oxidize alcohols is with copper (II) oxide. Upon heading, copper wire (Cu0 ) in an open flame leads to the formation of copper (II) oxide. The copper (II) oxide is then reacted with an alcohol to form an aldehyde or ketone, copper (I) oxide and water are products of the reactions.
\[ \text{Primary alcohol} \ce{->[\text{[O]}] Aldehyde } \]
\[ \text{Secondary alcohol} \ce{->[\text{[O]}] Ketone } \]
Chemically aldehydes and ketones both contain a carbonyl carbon and thus have similar chemical reactivities. However, aldehydes are more susceptible to oxidation because of the hydrogen atom attached to the carbonyl group. This is the basis for distinguishing between these two classes of compounds. Several tests are useful for differentiating between aldehydes and ketones.
The first test is referred to as the Tollens' or the Silver Mirror test. The Tollens test uses Ag+ ions to oxidize the aldehyde, as a result the silver ions are reduced to silver metal and either plated out on the surface of the reaction container, or forms a dark silver metal precipitate.
A second test for differentiating aldehydes and ketones is the Fehling's test. The Fehling's reagent uses Cu+2 ions to oxidize the aldehyde. The copper ions are reduced to form copper (I) oxide a reddish precipitate.
A stronger oxidant such as chromic acid which was used previously to oxidize alcohols can also be used to oxidize aldehydes. The chromic acid in the Bordwell-Wellman reagent is an orangeyellow solution that is reduced to Cr3+ which is a green color.
The last test is very specific for methyl ketones which are reacted with iodine (I2) in the presence of a strong base to form iodoform (iodomethane) which is insoluble in water and forms yellow crystals. The resulting iodoform has an odor similar to chloroform.
Experimental Procedures
Safety
WEAR YOUR SAFETY GOGGLES and GLOVES
Materials
Test tubes, test tube rack, disposable pipettes, ethanol, 1-butanol, 2-butanol, t-butyl alcohol, cyclohexanol, 1-hexanol, octanol.
Properties of alcohol
Solubility Tests - Water
Test the solubility of each of the listed substance with water by adding 10 drops of the substance to be tested to 3 mL of water in a test tube. Mix each of the test tubes vigorously for 15 seconds. Wait 30 seconds. Record your observations. Note which pairs are miscible and which are not.
Repeat the above test on your unknown sample. Dispose of the solutions in the waste bottle indicated by your instructor.
Oxidation of Primary and Secondary Alcohols
Jones Oxidation
Materials: test tubes, tube rack, DI-water, ethanol, 1-butanol, 2-butanol, t-butyl alcohol, cyclohexanol, Jones reagent
In a test tube place 15 mg or 10 drops of each alcohol and add 2 drops of Jones reagent (chromic acid in sulfuric acid) to the tube. Observe the color change as you add the chromic solution to the test tube. A color change within 15 seconds indicates a positive test for a primary or secondary alcohol. No color change indicated no reaction has occurred. Note that aldehydes also give a positive test, but tertiary alcohols do not. The Jones reagent will already be prepared for you. Record your observations.
Repeat the above test on your unknown sample. Record your observations.
Iodoform Test for Methyl Ketones
Materials: test tubes, tube rack, 3 M sodium hydroxide, warm water bath, iodine solution, acetone, butanal, 2-butanone, cyclohexanone, benzaldehyde, stoppers
Obtain and label six test tubes place 2 mL of water in each of the six separate test tubes. Add 4 drops or 20 mg of solid to the test tubes. Add 20 drops of 3 M NaOH to each, slowly add 40 drops of iodine solution. Stopper the test tube and shake vigorously, the formation of a yellow solid precipitate indicates a positive test. Record your observations.