Double bond reaction with bromine

This vinyl ether is monomeric in character and is used as a chemical intermediate or os o crosslinking ogent. Addition of isocyanic acid produces secondary diisocyonates. Divinyl ethers hydrolyze to the glycol and acetaldehyde. Chlorine or bromine odd to the double bonds. Reaction with an alcohol in the presence of water produces a diacetal. Polymerization of divinyl ether of diethylene glycol with acidic catolysts produce crasslinked gels. Unsoturoted polyesters, crosslinked with styrene, hove been made noncorrosive to metols through use of divinyl ethers to reduce hydroxyl ond acid numbeis. 

The reaction with bromine is very rapid and is easily carried out at room temperature, although the reaction is reversible under some conditions. In the case of bromine, an alkene-Br2 complex has been detected in at least one case. Bromine is often used as a test, qualitative or quantitative, for unsaturation. The vast majority of double bonds can be successfully brominated. Even when aldehyde, ketone, amine, so on functions are present in the molecule, they do not interfere, since the reaction with double bonds is faster. 

The Wittig reaction can bo used for the double bond and with benzylic bromination In mind wc prefer phosphonium salt (15), bromide (16), and hence available acid (17) as starting materials. 

An analogue of amitriptyline which contains an additional double bond in the central seven membered ring shows much the same activity as the prototype. Treatment of dibenzocycloheptanone 7 with N-bromosuccinimide followed by triethyl amine serves to introduce the additional double bond by the bromination-dehydrohalogenation sequence. Reaction of the carbonyl group with the Grignard reagent from 3-chloropropyl-N,N-dimethyl amine serves to introduce the side chain (73). Acid catalyzed dehydration affords the antidepressant compound cyclobenzaprine (74). ... 

Compound D has m/e equal to 130, so the compound (at 134) has increased by four hydrogen atoms (CjqHj,). You now know the formulas for all three unknowns. You also know that D has either a carbon-carbon triple bond or two carbon-carbon double bonds. The reaction with bromine in carbon tetrachloride confirms this. 

FIGURE 23.1 The reactions of ethylene and menthene with bromine. In both molecules, electrostatic potential maps show similar polarity patterns for the carbon-carbon double bond functional group. Bromine therefore reacts with both in the same way, regardless of the size and complexity of the remainder of the molecule. 

In the above discussion of stereoselectivity the mechanisms of various reactions have been used to rationalize why some are stereoselective and some are not. Thus the bromination of olefins proceeds via a bridged bromonium ion intermediate and gives only trails addition across the double bond [reactions (6.2) and (6.3)]. In contrast, the addition of HBr across a double bond gives a carboca-tion intermediate that does not maintain the facial integrity of the olefin and is thus much less stereoselective [reaction (6.1)]. In these examples the mechanism of the reaction is used to explain and understand the diastereoselectivity that is observed. There are many other examples (usually in textbooks) where the mechanism of a reaction is used to rationalize the stereoselectivity of the process. To do this requires that the mechanism be known with certainty. 

However, if reaction does involve bromine atoms as intermediates, one would expect to find products (including acetolysis) derived from addition of these radicals to the double bond, especially with olefms, such as norbornene, that possess unreactive allylic positions. Obviously the detailed mechanism of this reaction remains to be resolved. 

The reaction with bromine is a classical test for the presence of double (or triple) bonds in an unknown compound. In the test, the unknown is added dropwise to a solution of bromine in a solvent such as CC14 or CH2C12. The bromine solution has a red-brown color. If the unknown contains carbon-carbon double or triple bonds, the addition reaction is nearly instantaneous. Because the addition products are colorless, the rapid disappearance of the bromine color constitutes a positive test for the presence of unsaturation. 

To explain this reaction, consider the fact that, due to the overlapping p orbitals, double bonds are electron rich. This property allows olefins, under certain conditions, to act as nucleophiles. In the case of a double bond reacting with molecular bromine, the result is formation of a three-membered ring containing a positively charged bromine atom. This three-membered ring is known as a bridged bromonium ion. Concurrent to formation... 

Although aromatic hydrocarbons are unsaturated, they have very different chemical properties to alkenes and allies. For example, benzene doesn t undergo an addition reaction with bromine despite having a double bond. 

The reaction is not particularly useful for preparation of enolizable a-diketones. The main complication is that the liberated trimethylsilyl bromide reacts with the newly formed enolic function, thus giving rise to a new double bond to which bromine can be added. Thus several bromination products of the a-diketones together with decomposition products are formed. 

The vinyl derivative was converted to ethynyl-CTM by reaction with bromine followed by HBr elimination. The double bond of vinyl-CTM turned out to be much less active than that in the ferrocene analog as regards electrophilic addition. Also, the stabilization of an a-carbonium center, the phenomenon characteristic of ferrocenyl cation, was not found in the manganese compound (379). 

Dilithio-1-alkenes 81 on the other hand show a clean reaction with bromine even at —90 °C interestingly without addition to the double bond taking place e-g. 

The first so-called aromatic compounds to be studied seriously, such as vanillin (derived from vanilla), had two obvious properties. They had a sweet smell and were remarkably stable. This last property was the reef on which many of the early theories of chemical bonding foundered. Consider benzene. Kekule knew that its molecular formula was C H. The only way he could rationalise this formula with the known properties of benzene, was to imagine the six carbon atoms joined in a ring and connected by three alternate double bonds. This is where the trouble started because double bonds are supposed to confer reactivity on an organic molecule benzene is stable. Double bonds can readily be added to for example, they will undergo fast reactions with bromine and sulphuric acid to give simple "addition" compounds. The reagents simply "add" across the double bond. 

By studying the perchloric acid-catalysed acetolysis of the exo- and endo-[2- H]-alcohols (323), Friedrich and Cooper have established that cyclopropylcarbinyl rearrangement does occur in bicydo [n, 1,0]alkane systems. Electrophilic addition to the double bond of vinylcyclopropanes leads to products with retained (major) and rearranged (minor) skeletons. Reactions with bromine and chlorine as well as... 

Compounds containing double bonds react with a bromine solution (red) to decolorize it. Similarly, they react with a solution of potassium permanganate (purple) to discharge its color and produce a brown precipitate (MnOj). These reactions are often used as qualitative tests to determine the presence of a double bond in an organic molecule (see Experiment 53). Both tests will be performed on the 4-meth-ylcyclohexene formed in this experiment. 

Not all double bonds react with the bromine solution. Only those that are electron-rich are sufficiently reactive nucleophiles to initiate the reaction. A double bond that is substituted by electron-withdrawing groups often fails to react or reacts slowly. Fumaric acid is an example of a compound that fails to give the reaction. 

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