An alkane sometimes known as paraffin which is a historical term having multiple meanings is the acyclic saturated hydrocarbon in organic chemistry. To put it another way, the alkane is made up of hydrogen and carbon atoms arranged in the tree structure having single carbon and carbon bonds. Alkanes have the typical chemical formula CnH2n+2. The alkanes range in complexity from the most basic, n = 1 (often referred to as the parent molecule), such as methane (CH4), to arbitrarily huge and complicated compounds. 6-ethyl-2-methyl-5-(1-methyl ethyl) octane (C50H102) or pentacontane (C50H102)
“Acyclic branched or unbranched hydrocarbons with the general formula CnH2n+2, and hence consisting solely of hydrogen atoms and saturated carbon atoms,” according to the International Union of Pure and Applied Chemistry.
Despite having a distinct general formula, some sources use the term to refer to any saturated hydrocarbon, including those that are either monocyclic cycloalkane or polycyclic (i.e. cycloalkanes are CnH2n).
Each carbon atom is sp3-hybridized with four sigma bonds in an alkane, and each hydrogen atom is joined to one of the carbon atoms (in a C–H bond). The carbon skeleton or the carbon backbone of the molecule is the longest series of linked carbon atoms. The number of carbon atoms can be thought of as that of the alkane’s size.
About Grignard Reagents
The Grignard reagent is a chemical compound having the general formula of R−Mg−X, where X denotes the halogen atom and R is an organic group which is generally an alkyl or aryl hydrocarbon. They are the subclass of the organomagnesium compounds.
Preparation Of Alkane by Grignard Reaction
Grignard Reagents are a class of reagents developed by Grignard
Grignard reagents are formed when haloalkanes and other compounds containing a halogen atom bound to either sp3-hybridized or sp2-hybridized carbon atoms (aryl and vinyl halides) react with magnesium metal to produce organomagnesium halides. Diethyl ether (CH3CH2OCH2CH3) is commonly used to make Grignard reagents. The reaction requires the use of an ether solvent.
Although their reactivities varied, Grignard reagents are easy to make from 1°, 2°, and 3° alkyl halides. Aryl and vinyl halides react more slowly, therefore Grignard reagents of these compounds must be prepared with the cyclic ether tetrahydrofuran (THF). Because THF solvates the Grignard reagent better than diethyl ether, the cyclic ether provides more powerful reaction conditions, but the pace of the reaction also increases.
Two molecules of tetrahydrofuran, THF, are bonded to magnesium in this molecular model of a methyl-magnesium chloride complex, a Grignard reagent. The crystal structure serves as the basis for the model. I > Br > CI > > F is the order of halogen reactivity in haloalkanes. Grignard reagents are never made with organic fluorides because they are so unreactive. Grignard reagents are often made with organohalogen compounds containing bromine and chlorine, which are easily available. Synthetically, Grignard reagents are utilized to generate new carbon-carbon bonds. The carbon atom in a Grignard reagent has a partial negative charge, while the metal has a partial positive charge. The carbon–magnesium bond has the opposite polarity as the carbon–halogen bond in haloalkanes.
Grignard reagents resemble carbanion because their carbon atoms have a partial negative charge, and they react with electrophilic centers like the carbonyl carbon atom of aldehydes, ketones, and esters. Later chapters will go through this chemistry in detail. Please log in to download the full-size image. Acidic hydrogen atoms in compounds like alcohols and water react quickly with Grignard reagents. When a Grignard reagent combines with water, the halogen is replaced by a proton, and an alkane is formed. As a result, the Grignard reagent provides a two-step method for converting a haloalkane to an alkane. Please log in to download the full-size image. 9.7th Problem Formulate a CH3CH2CHDCH3 synthesis commencing with 1-butene and heavy water (D2O).
Grignard Reagent Preparation
The following points outline the procedure for preparing Grignard reagents. It should be noted that many of these reagents are also commercially available.
- These reagents are made by combining magnesium with organic halides such as alkyl or aryl halides.
- This is accomplished with the assistance of ether-based solvents (defined by the formula R-O-R’) because the ligands given by these solvents aid in the stability of the organomagnesium molecule.
- Water and air are extremely damaging to this synthesis and can quickly destroy the Grignard reagent that is being generated by protonolysis or reagent oxidation. As a result, the procedure must be carried out in an airless environment.
- When moist solvents are utilized with the use of ultrasound, the magnesium can be activated to make it consume water.
- The reaction can become highly exothermic after the slow induction stage. This is the one of the most critical considerations that is taken into care while manufacturing the Grignard reagent in a commercial setting.
- Aryl or alkyl chlorides, bromides, and iodides are among the organic halides employed in these processes. Aryl and alkyl fluorides are not widely employed because they are very reactive. The magnesium, on the other hand, can be activated using Rieke metals to make the fluoride more reactive.
Conclusion
A Grignard reagent is an extremely strong nucleophile and can behave like carbonyl compounds with electrophiles. Grignard Reagents Are Nucleophiles. Grignard reagents are one of the strong bases and will react with the protic compounds which makes them exceedingly valuable tools for organic synthesis.