Reactions of Hydrocarbons, Chemistry tutorial

Reactions of Hydrocarbons

PURPOSE:

  • To make out saturated and unsaturated hydrocarbons using properties and reactions. 
  • To learn substitution and calculation reactions.  

Equipments

                           Materials

Test tube rack (1)

Cyclohexane

  n-Hexane

Test tube holder (2)

0.50 % KMnO4

  Conc. H2SO4

100 mL beaker

Toluene

  Br2/CCl4 or Br2/CH2Cl2

Medium test tube (6)

  10 % Na2CO3

Unknown hydrocarbons

Discussion: 

The number of recognized organic compounds totals into the millions. Of such compounds, the simplest kinds are those that have only hydrogen and carbon atoms. Such are well-known as hydrocarbons. Since of the number and variety of hydrocarbons that can survive, several means of categorization is needed.

One means of classification based on the way in that carbon atoms are attached. Chain aliphatic hydrocarbons are compounds consisting of carbons associational either in a particular chain or in a branched chain. Cyclic hydrocarbons are aliphatic compounds that contain carbon atoms linked in a closed polygon (as well termed to as a ring). For instance, hexane (single) and 2-methylpentane (branched) are chain aliphatic molecules, whilst cyclohexene is a cyclic aliphatic compound.

715_cyclic aliphatic compound.jpg

An additional means of classification based on the kind of bonding that exists between carbons. Hydrocarbons that have only carbon-to-carbon single bonds are termed alkanes. Such are as well termed to as saturated molecules. Hydrocarbons containing at least one carbon-to-carbon double bond are called alkenes, and compounds through at least one carbon-to-carbon triple bond are termed alkynes. Alkenes and alkynes are referred to as unsaturated molecules. Lastly, a class of cyclic hydrocarbons that enclose a sealed loop (sextet) of electrons is termed aromatic. Through so many compounds possible, recognition of the bond kind is a significant step in founding the molecular structure. Rapid effortless tests on tiny examples can set up the physical and chemical properties of the compounds via class.

Several of the examined physical properties of hydrocarbons consequence from the nonpolar character of the compounds. In common, hydrocarbons don't mix through polar solvents such as water or ethanol (ethyl alcohol). Alternatively, hydrocarbons mix through comparatively nonpolar solvents these as ligroin (a mixture of alkanes), carbon tetrachloride (CCl4), or dichloromethane (CH2Cl2). Since the density of most hydrocarbons is less than that of water, they will drift. Crude oil and crude oil products (home heating oil and gasoline) are mixtures of hydrocarbons; whenever spilled on water, such materials extend rapidly alongside the surface since they are insoluble in water.

The chemical reactivity of hydrocarbons is finding out via the kind of bond in the compound. Unsaturated hydrocarbons (that is alkenes and alkynes) react via addition of reagents to the double or triple bonds. The addition products happen to saturated; by fragments of the reagent becoming joined the carbons of the multiple bonds. Aromatic compounds, through a superior carbon-to-hydrogen ratio than nonromantic compounds, undergo replacement in the presence of catalysts rather than a calculation reaction.

1. Reaction with bromine: 

Unsaturated hydrocarbons react speedily through bromine in a solution of carbon tetrachloride or cyclohexene. The reaction is the computation of the components of bromine to the carbons of thenumerous bonds.

1989_multiple bonds.jpg

The bromine solution is red; the product that has the bromine atoms connected to carbon is colorless. Therefore, a reaction has occurred when there is a loss of color from the bromine solution and a colorless solution stays. Since alkanes have simply single C- C bonds show, no reaction through bromine is examined; the red color of the reagent would persist whenever adjoined. Aromatic compounds oppose addition reactions since of their 'aromaticity': the possession of a sealed loop (sextet) of electrons that imparts tremendous stability. Such compounds can react through bromine but need the existence of a catalyst these as iron fillings or aluminum chloride.

2. Reaction with concentrated sulphuric acid:

Alkenes react through cold concentrated sulphuric acid via addition. Alkyl sulfonic acids form as products and are soluble in H2SO4; following water work-up consequences in an '-OH' on the more substituted carbon (as showed in lecture). 

391_Reaction with concentrated sulphuric acid.jpg

Saturated hydrocarbons are unreactive (calculations aren't possible); alkynes react gradually and need a catalyst (H2SO4); due to their inherent stability, aromatic compounds are as well unreactive.

3. Reaction with potassium permanganate:

Dilute or alkaline solutions of KMnO4 oxidize unsaturated compounds. Alkanes and aromatic compounds are normally unreactive. Evidence that a reaction has occurred is examined via the loss of the purple color of KMnO4 and the formation of the brown precipitate manganese dioxide,

2100_Reaction with potassium permanganate.jpg

Note that the product shaped (which encloses two '-OH' groups) is termed a glycol.

Experimental procedure: 

Suppose the organic compounds are extremely flammable. Utilize only little quantities. Carry on away from open flames. Suppose the organic compounds are toxic and can be absorbed through the skin. Avoid contact; wash if any chemical spills on our person. Handle focused sulphuric watchfully. Flush through water if any spills on our person. Potassium permanganate and bromine are toxic; bromine solutions are as well corrosive. Even though the solutions are diluted, they might reason burns to the skin. Wear gloves whenever working through such chemicals. As well consider the subsequent:

1. The hydrocarbons hexane, cyclohexene, and toluene (alkane, alkene and aromatic, respectively) are available in dropper bottles. 

2. The reagents 1% Br2 in cyclohexene, 1% aqueous KMnO4, and concentrated H2SO4 are obtainable in dropper bottles. 

3. Unknowns are in dropper bottles labeled A, B, and C. They might consist of an alkane, an alkene, and/or an aromatic compound. 

4. Test tubes will be appropriate for all the tests; mix carefully. 

5. Dispose of all organic throw away as directed via the instructor. Don't transfer them into the sink. 

Physical Properties of Hydrocarbons

1. Water solubility of hydrocarbons: Label 6 test tubes through the name of the material to be tested. Situate into each test tube 5 drops of the suitable hydrocarbon: hexane, cyclohexene, toluene, unknown A, unknown B, and unknown C. Add about 5 drops of water drop wise into each test tube. Water is a polar solvent. Is there any division of components? Which component is on the bottom; which component is on the top? Mix the contents. What occurs when the contents are permitted to settle? What do we terminate about the density of the hydrocarbon? Is the hydrocarbon denser than water or less dense than water? Record our examinations. Save such solutions for comparison by the next part.

2. Solubility of hydrocarbons in ligroin: Label 6 test tubes through the name of the material to be tested. Situate into each test tube 5 drops of the appropriate hydrocarbons: hexane, cyclohexene, toluene, unknown A, unknown B, and unknown C. Add about 5 drops of ligroin  drop wise  into each test tube. Ligroin is a nonpolar solvent. Is there a division of components? Is there a bottom layer and a top layer? Mix the substances. Is there some transform in the appearance of the contents before and after mixing? Compare these test tubes through those from the previous part. Record our observations. Can we build any termination about the density of the hydrocarbons from what we in fact see?

Chemical Properties of Hydrocarbons: 

i. Reaction by bromine:  consequences presented on data sheet.

ii. Reaction by KMnO4 (Baeyer's test): Label 6 clean, dry test tubes through the name of the material to be checked. Situate into each test tube 5 drops of the suitable hydrocarbon: hexane, cyclohexene, toluene, unknown A, unknown B, and unknown C. Watchfully adds (drop wise) 1% aqueous KMnO4 solution; after every drop, shake to mix up the solutions. Keep add up of the number of the drops required to contain the colour of the permanganate solution persist; don't add more than 10 drops. Record our examinations. 

i. Reaction through concentrated H2SO4:  Label 6 clean, dry test tubes through the name of the material to be tested. Situate into each test tube 5 drops of the suitable hydrocarbon: hexane, cyclohexene, toluene, unknown A, unknown B, and unknown C. Place all of the test tubes in an ice bath. Wear gloves and carefully add (by shaking) 3 drops of cold, concentrated sulphuric acid to each test tube. Note whether the solution has happen to homogeneous or whether a color is created. (The evolution of heat, the formation of a homogeneous solution, or the appearance of a color is verification that a reaction has happened.) Record our observations. 

ii. Unknowns: By comparing the observations we made for our unknowns through that of the known hydrocarbons, we can identify unknowns A, B, and C. Record their identities on our data sheet.

Data and results (properties of hydrocarbons):

Physical properties of hydrocarbons

Solubility: Does the hydrocarbon mix through the solvent, soluble, or not mix by solvent, insoluble? Utilize the observations we construct for the solubility tests and determine whether the hydrocarbons are polar or nonpolar substances.

Density: For water, is the density greater than water (sinks) or less than water (floats)? For ligroin, can we tell anything about the relative densities? H2O Ligroin

 

H2O

Ligroin

Hydrocarbon

 Solubility 

Density

Solubility

  Density

Hexane

 

 

 

 

Cyclohexene

 

 

 

 

Toluene

 

 

 

 

 

Unknown A 

 

 

 

 

Unknown B  

 

 

 

 

Unknown C  

 

 

 

 

Table: Chemical properties of hydrocarbons (Note: results for bromine test are presented) Hydrocarbn Bromine Test KMnO4 Test H2SO4 Test

Hydrocarbn

Bromine Test

KMnO4 Test

H2SO4 Test

Hydrocarbon

 

 

 

Hexane

 

 

 

Cyclohexene

 

 

 

Toluene

 

 

 

 

Unknown A 

 

 

 

Unknown B  

 

 

 

Unknown C  

 

 

 

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