Lab Report-Determining Reactions of Aldehydes and Ketones

Updated on April 17, 2016

Abstract

The aim of this experiment was to identify which functional groups the various chemicals and unknown substances belonged to using the different reaction tests. The main purpose was to determine the reactions of Aldehydes and Ketones. Aldehydes and Ketones are organic compounds consisting of the carbonyl functional group. Aldehydes contain their carbonyl group at the end of the carbon chain and are susceptible to oxidation while Ketones contain theirs in the middle of the carbon chain and are resistant to oxidation. Jones’s Test, Tollen’s Reagent and Iodoform Reaction were the three tests used to determine the reactions of aldehydes and ketones. The Chromic Anhydride test caused Aldehydes to turn blue, and Ketones orange. The Tollen’s Reagent test caused the oxidation of aldehydes thus forming a mirror-like image in the test tube rendering it a positive test and the Iodoform reaction produced a yellow precipitate in the test tube which concluded the presence of an aldehyde.

Introduction

The carbon-oxygen double bond is one of the most important functional groups, due to its ubiquity, which are involved in most important biochemistry processes. Reactivity of this group is ruled by the electron imbalance in the πorbitals of the bond between a more electronegative and a carbon atom. This carbon atom is more likely to undergo a nucleophillic attack, especially if the oxygen is protonated. If the carbonyl group has hydrogen’s in the α-position, it can tautomerise to the enol, thus, Keto tautomer can become Enol tautomer.

Aldehydes and Ketones are organic compounds that consist of the carbonyl functional group, C=O. The carbonyl group that consists of one alkyl substituent and one hydrogen is the Aldehyde and those containing two alkyl substituents are called Ketones. These two organic compounds undergo reactions that are related to the carbonyl group, however,

, they can be distinguished due to their “susceptibility to oxidation” (1)

The carbonyl of an aldehyde is always at the end of the carbon chain whereas the carbonyl of a Ketone can lie anywhere within the carbon chain. These two organic compounds are found abundantly in nature. Since the carbonyl group is polar, aldehydes and ketones have a larger dipole moment. In the carbonyl group, the positive carbon atom will be attacked by nucleophiles. (1)

Addition reactions can be undergone by carbonyl groups. Since Aldehydes have the hydrogen atom attached to it, it makes them more susceptible to oxidation, which is the loss of electrons. However, Ketones lack the hydrogen atom in their carbonyl group and are therefore resistant to oxidation. Small Aldehydes and Ketones are easily dissolved in water but as the chain increases in length, its solubility decreases. (1)

In this experiment, the Chromic Anhydride (Jones’s Test), Tollen’s Reagent and the Iodoform reaction were used to test for the presence of aldehydes and ketones. Jones’s Test is an organic reaction for the oxidation of alcohols to carboxylic acids and ketones. This oxidation is very rapid and exothermic with high yields. Tollen’s Reagent was used to determine whether a substance is an aldehyde or ketone, which shows that aldehydes are easily oxidized while ketones are not. The Iodoform reaction would have a positive result if there is a pale yellow precipitate.

The aim of this experiment was to identify the reactions of Aldehydes and Ketones and which functional groups the unknown substances and known chemicals belonged to, using the different reaction tests.

Materials and Method

Chromic Anhydride (Jones’s Test)

Methanol, Isopropanol, Butanol, Ethanol, Tertiary butanol, Benzaldehyde, Cyclohexane and Secondary butanol, including all unknown samples (A and B) were used. One drop of carbonyl compound was added to 1 ml of acetone in a test tube. A drop of the chromic anhydride reagent was then added, and mixed to observe if the test distinguished aldehydes from ketones

Tollen’s Reagent

Two drops of 10% NaOH was added to 10 ml of 0.3 M aqueous silver nitrate and mixed sufficiently. This was added slowly, together with shaking a dilute solution of ammonia until the precipitate just dissolved. An excess of ammonia should be avoided. This is Tollen’s Reagent.

All the samples including the unknowns were used. A drop of carbonyl compound was added to 1 ml of Tollen’s Reagent in a test tube which was then shaken well, and left aside for 10 minutes. The test was positive if there is a formation of a silver mirror on the tube, or a black precipitate of silver. Heat for 5 minutes in a boiling water bath if the test is negative and re-observe.

Tollen’s reagent forms an explosive precipitate if it stands even for a few hours hence it should be disposed of immediately.

Iodoform Reaction

The samples used were acetone, cyclohexanone, benzaldehyde, ethanol, methanol, isopropanol and an unknown A.

Three drops of sample was added to 1 ml of water in a test tube. Three ml of 10% NaOH was then added using a pipette. Iodine-potassium reagent was then added drop wise until a faint color of iodine persists. It was left to stand for 3 minutes. The tube was heated for 5 minutes at 60ºC if no precipitate formed. More iodine was added if the faint color disappeared. The excess iodine was removed by added NaOH drop wise with an equal volume of water together with shaking and allowing it to stand for 10 minutes.

If a yellow precipitate formed, the test is considered positive.

Results

Chromic Anhydride (Jones’s test)

Jones’s reagent reacts with primary, secondary alcohols and aldehydes. Primary alcohols are oxidized to aldehydes while secondary alcohols are oxidized to ketones.

Table 1: Substances used and the observations that were made

Substance

Observation

Methanol

Black precipitate, blue murky solution

Isopropanol

Dark blue precipitate. Milky blue solution

Butanol

Murky blue solution, black precipitate

Ethanol

Milky blue solution. No precipitate

Unknown A

Milky blue solution. Black precipitate

Unknown B

Grey-blue precipitate. Yellow, oily top layer

Tertiary butanol

Orange-yellow solution. No precipitate.

Benzaldehyde

Clear solution, blue precipitate

Cyclohexane

Murky yellow solution

Secondary butanol

Blue, murky solution. Black precipitate

Unknown A could have been a primary alcohol, Secondary Butanol or an aldehyde since the color changed to blue.

Tollen’s Reagent

Tollen’s reagent shows that aldehydes are more easily oxidized while ketones are not. Tollen’s reagent consists of basic aqueous solution that contains silver ions. The reagent oxidizes and aldehyde into a carboxylic acid by the reduction of silver ions into metallic silver and forms a mirror-like image on the test tube. Tollen’s reagent does not oxidize ketones, therefore, the test tube containing a ketone does not form a mirror-like image.

Table 2: list of positive and negative Tollen’s reagent tests

Chemical

Observation + Test

Methanol

No reaction – Negative

Isopropanol

No reaction – Negative

Butanol

No reaction – Negative

Acetaldehyde

Silver – Positive

Acetone

No reaction – Negative

Propanol

No reaction – Negative

Ethanol

No reaction – Negative

Unknown A

No reaction – Negative

Unknown B

Black precipitate, white liquid - Positive

Tertiary butanol

No reaction – Negative

Benzaldehyde

Grey - Negative

Cyclohexanone

Slightly yellow liquid - Negative

Secondary butanol

No reaction – Negative

Proprion aldehyde

Silver - Positive

Acetaldehyde formed a precipitate which was silver before it was heated. Unknown B formed a mirror-like image 2 minutes after heating. Other chemicals formed no precipitate.

Iodoform reaction

Table 3: The results obtained during the Iodofrom reaction

Chemical

Observation

Methanol

No reaction

Isopropanol

Cloudy yellow. No precipitate

Acetone

No reaction. Should have precipitated

Ethanol

Cloudy yellow. No precipitate

Unknown A

Cloudy yellow. No precipitate

Unknown B

Cloudy yellow. No precipitate

Benzaldehyde

Yellow precipitate

Cyclohexanone

No reaction. Should have precipitated

Discussion

In order to be able to identify an organic compound, it needs to show the same physical and chemical properties as the known compound.

Chromic Anhydride (Jones’s Test)

The Jones reagent is a mixture of chromic anhydride and dilute sulfuric acid (CrO3 + H2SO4 + H2O) in acetone. It is used in the oxidation of secondary alcohols that do not contain acid sensitive groups, to corresponding ketones. Since the oxidation is practically instantaneous, it was encouraged to investigate its usefulness as a qualitative test to distinguish tertiary alcohols from primary or secondary alcohols. It appears to be ideally suited for this purpose.

In this experiment, Aldehydes turned blue in color as they are more susceptible to oxidation under Jones’s Test conditions, and can undergo nucleophillic reactions. They only have one alkyl group that can donate electrons whereas Ketones turned orange in color as they are less reactive and susceptible to nucleophillic reactions as they contain two alkyl substituents.

Unknown A could have been a primary alcohol, Secondary Butanol or an aldehyde since the color changed to blue. Tertiary Butanol changed to orange, thus, rendering it a Ketone.

Tollen’s Reagent

Tollen's reagent is a chemical reagent used to determine the presence of an aldehyde or α-hydroxyl ketone functional groups. The reagent consists of a solution of silver nitrate and ammonia. A positive test with Tollen's reagent is indicated by the precipitation of elemental silver, often producing a characteristic "silver mirror" on the inner surface of the reaction vessel.

Since Aldehydes have the presence of hydrogen atoms, it makes it easier for it to be oxidized, hence forming the mirror-like image on the test tubes. This can be seem in Acetaldehyde as well as Proprion aldehyde as the have formed the silver substance. These chemicals have therefore tested positive to Tollen’s Reagent. The majority of the chemicals that tested negative are said to be Ketones as no reaction had occurred. There was no change to the colorless solution due to Ketones being less susceptible to oxidation.

Iodoform Reaction

A positive result of this test would be indicated by a pale yellow precipitate in the test tube. Chemicals that tested positive to this test include Benzaldehyde. Isopropanol, ethanol and unknown substance A and B produced a cloudy yellow solution with no precipitate and therefore test negative.

The presence of hydroxide ions is important for the reaction to happen - they take part in the mechanism for the reaction. The methyl group of the ketone is then removed from the molecule to produce iodoform (CHI3).


References

  1. Lawrence, N. J. (1937). Journal of the Chemical Society, 59, 760-761
  2. William, E.B, Gabriella, S. Louise, Z. Yang and Huges, D.E. (December 2011). Journal of chemical Research. 55, 675-677

Questions & Answers

    Comments

      0 of 8192 characters used
      Post Comment

      • profile image

        Purity 

        2 weeks ago

        Thanks so helpful in my lab report

      • profile image

        RODRICK KUDEKO 

        4 weeks ago

        it is really helpful thanks

      • Yaseeny15 profile imageAUTHOR

        Yaseen Essack 

        3 months ago from South Africa

        It's a pleasure.

      • profile image

        Phelix otieno 

        3 months ago

        Thanks for the information

      • profile image

        Yande Musonda 

        3 months ago

        Thanks for the help

      • Yaseeny15 profile imageAUTHOR

        Yaseen Essack 

        5 months ago from South Africa

        Hi Sammy and Paschal.

        I appreciate the feedback

        Thank You

      • profile image

        sammy silva 

        5 months ago

        thanks alot for this report

      • profile image

        Paschal Nicodemus John 

        7 months ago

        The practical was good performed

      • Yaseeny15 profile imageAUTHOR

        Yaseen Essack 

        14 months ago from South Africa

        I am glad it helped kiokote. I have some new reports that I will be posting. If u need anything, please feel free to contact me.

      • profile image

        kiokote 

        14 months ago

        i happy when i get my problems solved here

      • Yaseeny15 profile imageAUTHOR

        Yaseen Essack 

        15 months ago from South Africa

        Thank You Nyonzwe

        I'm glad it helped. Please feel free to contact me if you have any questions.

      • profile image

        NYONZWE 

        15 months ago

        MATERIAL HAS,REALLY HELPED ME,THANKS ALOT

      working

      This website uses cookies

      As a user in the EEA, your approval is needed on a few things. To provide a better website experience, owlcation.com uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

      For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at: https://owlcation.com/privacy-policy#gdpr

      Show Details
      Necessary
      HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
      LoginThis is necessary to sign in to the HubPages Service.
      Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
      AkismetThis is used to detect comment spam. (Privacy Policy)
      HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
      HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
      Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
      CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
      Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the googleapis.com or gstatic.com domains, for performance and efficiency reasons. (Privacy Policy)
      Features
      Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
      Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
      Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
      Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
      Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
      VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
      PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
      Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
      MavenThis supports the Maven widget and search functionality. (Privacy Policy)
      Marketing
      Google AdSenseThis is an ad network. (Privacy Policy)
      Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
      Index ExchangeThis is an ad network. (Privacy Policy)
      SovrnThis is an ad network. (Privacy Policy)
      Facebook AdsThis is an ad network. (Privacy Policy)
      Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
      AppNexusThis is an ad network. (Privacy Policy)
      OpenxThis is an ad network. (Privacy Policy)
      Rubicon ProjectThis is an ad network. (Privacy Policy)
      TripleLiftThis is an ad network. (Privacy Policy)
      Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
      Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
      Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
      Statistics
      Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
      ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
      Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)