Jet fuels from Biomass

Biomas can be transformed into long chain jet and diesel fuel Link to the original Article: Production of liquid hydrocarbon transportation fuels by oligomerization of biomass-derived C9 alkenes David Martin Alonso, Jesse Q. Bond, Juan Carlos Serrano-Ruiz and James A. Dumesic, Green Chem., 2010, 12, 992 DOI: 10.1039/c001899f

Making fuels from biomass waste

4 step process produces heavy alkanes suitable for diesel

For full story :

Making fuels from biomass waste

Nobel Prize 2010 for palladium-catalysed cross-coupling

The 2010 Nobel prize for chemistry has been awarded to three pioneers of synthetic organic chemistry whose eponymous reactions have become ubiquitous and indispensible.

Richard Heck of the University of Delaware in Newark, US, Ei-ichi Negishi of Purdue University, US, and Akira Suzuki of Hokkaido University in Japan, independently developed palladium-catalysed cross-coupling reactions as a way to forge new carbon-carbon bonds with precision and under mild reaction conditions. Heck, Negishi and Suzuki reactions are now used universally in every organic synthesis laboratory across the world, as well as in major industrial processes.

The three chemists have been working in the field for decades, and if there is one surprise about their being awarded the prize, it is perhaps that it didn't come sooner.

Richard Heck, Ei-ichi Negishi and Akira Suzuki share the Nobel Prize in Chemistry 2010

Heck published a series of papers in 1968 reporting the addition of methyl and phenylpalladium halides to olefins at room temperature. A further step allowed the unprecedented alkylation of an olefin. In 1976 Negishi investigated the palladium-catalysed cross-coupling of organometallic species with organohalides, eventually demonstrating that organozinc compounds could permit highly selective reactions under mild conditions and in the presence of a range of functional groups. Suzuki focused on organoboron compounds, demonstrating in 1979 that such species in the presence of a base could be cross coupled with vinyl and aryl halides in the presence of a palladium catalyst.

In subsequent years these reactions were improved and modified to become indispensible tools for the organic chemist and have been used to synthesise a range of complex natural products which would otherwise remain extremely difficult if not impossible to make.

Speaking from his home in the US at 6am, having been awoken an hour earlier with news of the prize, Negishi pronounced himself 'extremely happy - this means a lot.' He conceded that he knew the award of the Nobel Prize was a possibility, and indeed had been a long-held ambition. 'There had been some mumblings and I did begin to think of this and that,' he laughed. 'I have been dreaming about this prize for half a century, since I came to America and encountered several Nobel laureates, when I realised it was not a story - it was a reality which in principle could happen to anyone, including myself.'

Negishi added, 'I have accomplished half my goal. I would like to keep working for at least several more years.'

Guy Lloyd-Jones, a synthetic organic chemist at the University of Bristol in the UK, says that the trio are 'extremely worthy' winners. 'It is hard now to pick up an issue of any mainstream chemistry journal that features organic synthesis which does not contain a number of papers in which these reactions have been used. These reactions have revolutionised our ability to make selective carbon-carbon bonds. The prize is absolutely deserved and the only question that some people have asked is why it has taken so long.'

SUZUKI CROSS-COUPLING

In 1979, A. Suzuki and N. Miyaura reported the stereoselective synthesis of arylated (E)-alkenes by the reaction of 1- alkenylboranes with aryl halides in the presence of a palladium catalyst. The palladium-catalyzed cross-coupling reaction between organoboron compounds and organic halides or triflates provides a powerful and general method for the formation of carbon-carbon bonds known as the Suzuki cross-coupling. There are several advantages to this method: 1) mild reaction conditions; 2) commercial availability of many boronic acids; 3) the inorganic by-products are easily removed from the reaction mixture, making the reaction suitable for industrial processes; 4) boronic acids are environmentally safer and much less toxic than organostannanes (see Stille coupling); 5) starting materials tolerate a wide variety of functional groups, and they are unaffected by water; 6) the coupling is generally stereo- and regioselective; and 7) sp3-hybridized alkyl boranes can also be coupled by the B-alkyl Suzuki-Miyaura cross-coupling. Some disadvantages are: 1) generally aryl halides react sluggishly; 2) by-products such as self-coupling products are formed because of solvent-dissolved oxygen; 3) coupling products of phosphine-bound aryls are often formed; and 4) since the reaction does not proceed in the absence of a base, side reactions such as racemization of optically active compounds or aldol condensations occur. Improvements of the Suzuki cross-coupling include the development of catalysts facilitating coupling of unreactive aryl halides, the ability to react sp3-hybridized alkyl halides, and the use of alkyl, alkenyl, aryl, and alkynyl trifluoroborates in place of boronic acids.

Mechanism:

The mechanism of the Suzuki cross-coupling is analogous to the catalytic cycle for the other cross-coupling reactions and has four distinct steps: 1) oxidative addition of an organic halide to the Pd(0)-species to form Pd(II); 2) exchange of the anion attached to the palladium for the anion of the base (metathesis); 3) transmetallation between Pd(II) and the alkylborate complex; and 4) reductive elimination to form the C-C sigma bond and regeneration of Pd(0). Although organoboronic acids do not transmetallate to the Pd(II)-complexes, the corresponding ate-complexes readily undergo transmetallation. The quaternization of the Aboron atom with an anion increases the nucleophilicity of the alkyl group and it accelerates its transfer to the palladium in the transmetallation step. Very bulky and electron-rich ligands (e.g., P(t-Bu)3) increase the reactivity of otherwise unreactive aryl chlorides by accelerating the rate of the oxidative addition step.

NEGISHI CROSS-COUPLING

In 1972, after the discovery of Ni-catalyzed coupling of alkenyl and aryl halides with Grignard reagents (Kumada cross-coupling), it became apparent that in order to improve the functional group tolerance of the process, theorganometallic coupling partners should contain less electropositive metals than lithium and magnesium. In 1976, E. Negishi and co-workers reported the first stereospecific Ni-catalyzed alkenyl-alkenyl and alkenyl-aryl cross-coupling of alkenylalanes (organoaluminums) with alkenyl- or aryl halides. Extensive research by Negishi showed that the best results (reaction rate, yield, and stereoselectivity) are obtained when organozincs are coupled in the presence of Pd(0)-catalysts. The Pd- or Ni-catalyzed stereoselective cross-coupling of organozincs and aryl-, alkenyl-, or alkynyl halides is known as the Negishi cross-coupling. The general features of the reaction are: 1) both Ni- and Pdphosphine complexes work well as catalysts. However, the Pd-catalysts tend to give somewhat higher yields and better stereoselectivity, and their functional group tolerance is better; 2) the active catalysts are relatively unstable Ni(0)- and Pd(0)-complexes but these can be generated in situ from more stable Ni(II)- and Pd(II)-complexes with a reducing agent (e.g., 2 equivalents of DIBAL-H or n-BuLi); 3) in the absence of the transition metal catalyst, the organozinc reagents do not react with the alkenyl halides to any appreciable extent; 4) the most widely used ligand is PPh3, but other achiral and chiral phosphine ligands have been successfully used; 5) the various organozinc reagents can be prepared by either direct reaction of the organic halide with zinc metal or activated zinc metal or by transmetallation of the corresponding organolithium or Grignard reagent with a zinc halide (ZnX2); 6) the use of organozinc reagents allows for a much greater functional group tolerance in both coupling partners than in the Kumada cross-coupling where organolithiums and Grignard reagents are utilized as coupling partners; 7) other advantages of the use of organozincs include: high reactivity, high regio-, and stereoselectivity, wide scope and applicability, few side reactions and almost no toxicity; 8) the reaction is mostly used for the coupling of two C(sp2) carbons but C(sp2)-C(sp) as well as C(sp2)-C(sp3) couplings are well-known; 9) besides organozincs, compounds of Al and Zr can also be utilized; 10) if the organoaluminum and organozirconium derivatives are not sufficiently reactive, they can be transmetallated by the addition of zinc salts, and this protocol is referred to as the double metal catalysis; and 11) of all the various organometals (Al, Zr, B, Sn, Cu, Zn), organozincs are usually the most reactive in Pd-catalyzed cross-coupling reactions and do not require the use of additives (e.g., bases as in Suzuki crosscouplings) to boost the reactivity; Some of the limitations of the Negishi cross-coupling are: 1) propargylzincs do not couple well but homopropargylzincs do; 2) secondary and tertiary alkylzincs may undergo isomerization, but crosscouplings of primary alkyl- and benzylzincs give satisfactory results; and 3) due to the high reactivity or organozincs, CO insertion usually does not happen unlike in the case of less reactive organotins (see carbonylative Stille crosscoupling).

Mechanism:

HECK REACTION

In the early 1970s, T. Mizoroki and R.F. Heck independently discovered that aryl, benzyl and styryl halides react with olefinic compounds at elevated temperatures in the presence of a hindered amine base and catalytic amount of Pd(0) to form aryl-, benzyl-, and styryl-substituted olefins.1-3 Today, the palladium-catalyzed arylation or alkenylation of olefins is referred to as the Heck reaction. Since its discovery, the Heck reaction has become one of the most widely used catalytic carbon-carbon bond forming tools in organic synthesis. The general features of the reaction are: 1) it is best applied for the preparation of disubstituted olefins from monosubstituted ones; 2) the electronic nature of the substituents on the olefin only has limited influence on the outcome of the reaction; it can be either electron-donating or electron-withdrawing but usually the electron poor olefins give higher yields; 3) the reaction conditions tolerate a wide range of functional groups on the olefin component: esters, ethers, carboxylic acids, nitriles, phenols, dienes, etc., are all well-suited for the coupling, but allylic alcohols tend to rearrange; 4) the reaction rate is strongly influenced by the degree of substitution of the olefin and usually the more substituted olefin undergoes a slower Heck reaction; 5) unsymmetrical olefins (e.g., terminal alkenes) predominantly undergo substitution at the least substituted olefinic carbon; 6) the nature of the X group on the aryl or vinyl component is very important and the reaction rates change in the following order: I > Br ~ OTf >> Cl; 7) the R1 group in most cases is aryl, heteroaryl, alkenyl, benzyl, and rarely alkyl (provided that the alkyl group possesses no hydrogen atoms in the b-position), and these groups can be either electron-donating or electron-withdrawing; 8) the active palladium catalyst is generated in situ from suitable precatalysts (e.g., Pd(OAc)2, Pd(PPh3)4) and the reaction is usually conducted in the presence of monodentate or bidentate phosphine ligands and a base; 9) the reaction is not sensitive to water, and the solvents need not be thoroughly deoxygenated; and 10) the Heck reaction is stereospecific as the migratory insertion of the palladium complex into the olefin and the b-hydride elimination both proceed with syn stereochemistry. There are a couple of drawbacks of the Heck reaction: 1) the substrates cannot have hydrogen atoms on their b-carbons, because their corresponding organopalladium derivatives tend to undergo rapid-b-hydride elimination to give olefins; and 2) aryl chlorides are not always good substrates because they react very slowly. Several modifications were introduced during the past decade: 1) asymmetric versions; 2) generation of quaternary stereocenters in the intramolecular Heck reaction; 3) using water as the solvent with water-soluble catalysts;56,57,47 and 4) heterogeneous palladium on carbon catalysis.

Mechanism:

The mechanism of the Heck reaction is not fully understood and the exact mechanistic pathway appears to vary subtly with changing reaction conditions. The scheme shows a simplified sequence of events beginning with the generation of the active Pd(0) catalyst. The rate-determining step is the oxidative addition of Pd(0) into the C-X bond. To account for various experimental observations, refined and more detailed catalytic cycles passing through anionic, cationic or neutral active species have been proposed.

Challenging aqua regia's throne

Challenging aqua regia's throne

An 'organic' aqua regia which can selectively dissolve noble metals in solution has been discovered by researchers in the US. The finding could lead to new approaches to recycle noble metals such as gold and platinum from industrial processes and aid the manufacture of nanomaterials, says the team.

Traditional aqua regia is a mixture of concentrated nitric and hydrochloric acids in a ratio of 1:3 that can dissolve noble metals such as gold, palladium and palladium, even though the metals are not soluble in either acid alone. However, such inorganic acid compounds cannot be tuned to dissolve one noble metal and not another, making recycling noble metals with inorganic acids a challenge.

Now, Wei Lin and colleagues at the Georgia Institute of Technology in Atlanta, US, have demonstrated for the first time an organic solvent which achieves high dissolution rates of noble metals under mild conditions, with the added benefit of being tunable to a specific metal.

The teams organic aqua regia can selectively dissolve a range of noble metals

The team serendipitously discovered that gold dissolves when it is left in a mixture of thionyl chloride (SOCl₂) and the organic solvent pyridine. Further experiments on the system revealed that other organic solvents and reagents - such as N,N-dimethylformamide (DMF), imidazole, and pyrazine - could achieve similar effects when mixed with thionyl chloride, with the gold recoverable by subsequent calcination.

'Varying the recipe and reaction conditions even allows the selective dissolution of noble metals,' says Lin. For instance, a SOCl₂/DMF mixture dissolves gold but not palladium or platinum. 'The selectivity may be beneficial in improving the purity of the recycled noble metals from catalysis and the electronics industry,' Lin suggests.

'The spectacular dissolution selectivity relies on the intrinsic versatility of organic chemistry so that soon selective organic aqua regia mixtures will be used to dissolve the noble metal of interest,' says Mario Pagliaro a chemist at Italy's National Research Council (CNR). 'One immediate application will be full recovery of platinum from exhaust catalytic converters today, and from fuel cells tomorrow,' he suggests.

However, in terms of efficiency and cost, Lin concedes that his organic aqua regia is currently unable to compete with traditional aqua regia. But it does offer a safer alternative and it could have uses beyond recycling, such as synthesis of noble metal nanostuctures and selective removal of nanocoatings. 'It is still far from practical applications yet,' he admits.

The team is now working to further understand the chemistry of the dissolution process. 'There are a lot more interesting phenomena that we haven't published yet about organic aqua regia,' Lin adds.

Synthesis of Arylboronic Acid Ester

General Procedure for the Synthesis of Arylboronic acid ester from Arylboroic Acid with 2,2-Dimethyl-1,3-propanediol (5 mmol scale).

In a 50ml flask equipped with a stir-bar, arylboroic acid (5 mmol) and 2,2-dimethyl-1,3-propanediol (6 mmol) were combined. 15 mL dimethyl ether was added to the flask and the solution was stirred for 6 hours under room temperature. The dimethyl ether was then removed under vacuum to get the white solid mixture. The mixture was washed three times with water to remove the excess 2,2-dimethyl-1,3-propanediol. The product was dried at 50 ℃ under vacuum.

This method gave quantitative yield for 3 g scale.

Synthesis of Phenanthrone Derivatives from sec-Alkyl Aryl Ketones and Aryl Halides via a Palladium-Catalyzed Dual C−H Bond Activation and Enolate Cyclization - Journal of the American Chemical Society (ACS Publications)

A palladium-catalyzed chelation-assisted C−H activation of alkyl aryl ketones and their reaction with aryl iodides to afford ortho-arylated products is described. For sec-alkyl aryl ketones, the catalytic reaction proceeds further to give 10,10-dialkylphenanthrone derivatives. A possible reaction mechanism involving directed dual C−H bond activation and enolate cyclization for the formation of 10,10-dialkylphenanthrone derivatives is proposed.

Pd(II)-Catalyzed Hydroxyl-Directed C−H Activation/C−O Cyclization: Expedient Construction of Dihydrobenzofurans - Journal of the American Chemical Society (ACS Publications)

Pd(II)-Catalyzed Hydroxyl-Directed C−H Activation/C−O Cyclization: Expedient Construction of Dihydrobenzofurans - Journal of the American Chemical Society (ACS Publications)

Non-metal-catalysed C-C coupling

Non-metal-catalysed C-C coupling

Chinese chemists have successfully coupled aromatic molecules without the use of a transition metal catalyst - something that people have been trying to do for years with little success. Such cross-coupling reactions are crucial to organic synthesis and typically require expensive metals such as palladium. Efforts to find cheaper and more widely available alternatives have proved challenging.

Now, Wei Liu, from Wuhan University, and colleagues appear to have succeeded by using an organic catalyst, DMEDA (N,N'-dimethylethane-1,2-diamine) in the presence of the base potassium tert-butoxide. The team coupled unactivated benzene with a range of aryl iodides in the presence of the organic catalyst and the base.

"We have checked for contamination and excluded the involvement of trace amounts of transition metals" - Aiwen Lei, Wuhan University

The researchers suggest that the reaction proceeds via the formation of a radical, with the potassium salt initiating radical formation in the presence of DMEDA. 'In radical trap experiments the coupling was inhibited by a classical radical scavenger which suggested that radical species are involved,' says team member Aiwen Lei.

Could trace amounts of transition metal have contaminated the experiment? 'Obviously this is one of the most important factors,' says Lei. 'We have checked the contamination of trace amounts of transition metals by ICP [inductively coupled plasma atomic emission spectroscopy] and excluded the involvement of small amounts of transition metals in this transformation.' In addition, the potassium tert-butoxide used in the work was purified by sublimation to remove any contaminants.

Lei believes that the work could herald a new direction in organic synthesis. 'This is the first report of organocatalysis in carbon-carbon coupling or direct arylation between aryl halides and arenes, which could be considered as a conceptually different approach towards biaryl syntheses.'

Commenting on the work, Carsten Bolm, an organic synthesis expert from Aachen University in Germany, says, 'To be able to prepare cross-coupling products without the use of transition metals is an important scientific advance. Although at the present stage the substrate scope is by far too limited to make the process synthetically attractive, the findings illustrate that new reaction paths in direct C-H arylations are still to be discovered, and as such this work will be highly stimulating to the community.'

Characteristic IR Band Positions

Characteristic IR Band Positions

Group				Frequency Range (cm-1)
OH stretching vibrations
Free OH				3610-3645 (sharp)
Intramolecular H bonds				3450-3600 (sharp)
Intermolecular H Bonds				3200-3550 (broad)
Chelate Compounds				2500-3200 (very broad)
NH Stretching vibrations
Free NH				3300-3500
H bonded NH				3070-3350
CH Stretching vibrations
=-C-H				3280-3340
=C-H				3000-3100
C-CH3				2862-2882, 2652-2972
O-CH3				2815-2832
N-CH3 (aromatic)				2810-2820
N-CH3 (aliphatic)				2780-2805
CH2				2843-2863,2916-2936
CH				2880-2900
SH Stretching Vibrations
Free SH				2550-2600
C=-N Stretching Vibrations
Nonconjugated				2240-2260
Conjugated				2215-2240
C=-C Stretching Vibrations
C=-CH (terminal)				2100-2140
C-C=-C-C				2190-2260
C-C=-C-C=-CH				2040-2200
C=O Stretching Vibrations
Nonconjugated				1700-1900
Conjugated				1590-1750
Amides				~1650
C=C Sretching Vibrations
Nonconjugated				1620-1680
Conjugated				1585-1625
CH Bending Vibrations
CH2				1405-1465
CH3				1355-1395, 1430-1470
C-O-C Vibrations in Esters
Formates				~1175
Acetates				~1240, 1010-1040
Benzoates				~1275
C-OH Stretching Vibrations
Secondary Cyclic Alcohols				990-1060
CH out-of-plane bending vibrations    in substituted ethylenic systems
-CH=CH2				905-915, 985-995
-CH=CH-(cis)				650-750
-CH=CH-(trans)				960-970
C=CH2				885-895
Characteristic IR Absorption Frequencies of Organic Functional Groups
Functional Group		Type of Vibration	Characteristic Absorptions (cm-1)		Intensity
Alcohol
O-H		(stretch, H-bonded)	3200-3600		strong, broad
O-H		(stretch, free)	3500-3700		strong, sharp
C-O		(stretch)	1050-1150		strong
Alkane
C-H		stretch	2850-3000		strong
-C-H		bending	1350-1480		variable
Alkene
=C-H		stretch	3010-3100		medium
=C-H		bending	675-1000		strong
C=C		stretch	1620-1680		variable
Alkyl Halide
C-F		stretch	1000-1400		strong
C-Cl		stretch	600-800		strong
C-Br		stretch	500-600		strong
C-I		stretch	500		strong
Alkyne
C-H		stretch	3300		strong,sharp
		stretch	2100-2260		variable, not present in symmetrical alkynes
Amine
N-H		stretch	3300-3500		medium (primary amines have two bands; secondary have one band, often very weak)
C-N		stretch	1080-1360		medium-weak
N-H		bending	1600		medium
Aromatic
C-H		stretch	3000-3100		medium
C=C		stretch	1400-1600		medium-weak, multiple bands
Analysis of C-H out-of-plane bending can often distinguish substitution patterns
Carbonyl		Detailed Information on Carbonyl IR
C=O		stretch	1670-1820		strong
(conjugation moves absorptions to lower wave numbers)
Ether
C-O		stretch	1000-1300 (1070-1150)		strong
Nitrile
CN		stretch	2210-2260		medium
Nitro
N-O		stretch	1515-1560 & 1345-1385		strong, two bands

IR Absorption Frequencies of Functional Groups Containing a Carbonyl (C=O)
Functional Group	Type of Vibration	Characteristic Absorptions (cm-1)	Intensity
Carbonyl
C=O	stretch	1670-1820	strong
(conjugation moves absorptions to lower wave numbers)
Acid
C=O	stretch	1700-1725	strong
O-H	stretch	2500-3300	strong, very broad
C-O	stretch	1210-1320	strong
Aldehyde
C=O	stretch	1740-1720	strong
=C-H	stretch	2820-2850 & 2720-2750	medium, two peaks
Amide
C=O	stretch	1640-1690	strong
N-H	stretch	3100-3500	unsubstituted have two bands
N-H	bending	1550-1640
Anhydride
C=O	stretch	1800-1830 & 1740-1775	two bands
Ester
C=O	stretch	1735-1750	strong
C-O	stretch	1000-1300	two bands or more
Ketone
acyclic	stretch	1705-1725	strong
cyclic	stretch	3-membered - 1850 4-membered - 1780 5-membered - 1745 6-membered - 1715 7-membered - 1705	strong
,-unsaturated	stretch	1665-1685	strong
aryl ketone	stretch	1680-1700	strong

A good general reference for more detailed information on interpretation of infrared spectra (as well as other spectroscopic techniques) is Silverstein, R.M.; Bassler, G.C.; and Morrill, T.C.Spectrometric Identification of Organic Compounds. 4th ed. New York: John Wiley and Sons, 1981. QD272.S6 S55