Abstract:
Novel trivalent organophosphonite ligands having the structure of general formula (I): 
                                 
wherein R is an alkyl or aryl group containing 1 to 30 carbon atoms; Ar 1  and Ar 2  are aryl groups containing 4 to 30 carbon atoms; R1 to R6 are H or alkyl or aryl hydrocarbon radicals containing 1 to 40 carbon atoms; and X is a connecting group or a simple chemical bond, were developed and found to be very active for hydroformylation processes for ethylenically unsaturated substrates. Catalyst solutions prepared from these ligands with a Rh metal show an unusual “ligand acceleration effect” for simple alkenes, i.e., the hydroformylation activity increases as the concentration of ligand increases, and are capable of producing linear or branched aldehydes under typical hydroformylation conditions.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Ser. No. 61/016,665 filed on Dec. 26, 2007, the disclosure of which is incorporated herein by reference to the extent it does not contradict the disclosures herein. 
    
    
     FIELD OF THE INVENTION 
     This invention generally relates to phosphonite compounds, a catalyst solution containing the same, and a hydroformylation process using the catalyst solution. 
     BACKGROUND OF THE INVENTION 
     The hydroformylation reaction, also known as the oxo reaction, is used extensively in commercial processes for the preparation of aldehydes by the reaction of one mole of an olefin with one mole each of hydrogen and carbon monoxide. One use of the reaction is in the preparation of normal- and iso-butyraldehyde from propylene. The ratio of the amount of the normal aldehyde product to the amount of the iso aldehyde product typically is referred to as the normal-to-iso (N:I) or the normal-to-branched (N:B) ratio. In the case of propylene, the normal- and iso-butyraldehydes obtained from propylene are in turn converted into many commercially valuable chemical products such as, for example, n-butanol, 2-ethyl-hexanol, n-butyric acid, iso-butanol, neo-pentyl glycol, 2,2,4-trimethyl-1,3-pentanediol, and the mono-isobutyrate and di-isobutyrate esters of 2,2,4-trimethyl-1,3-pentanediol. 
     In most cases, a phosphorus ligand-containing catalyst is used for the oxo process (so called “low pressure hydroformylation process”). Phosphorus ligands not only can stabilize metal, but can also regulate the catalyst activity and selectivity. Oxo catalyst activity often decreases as the amount of phosphorus ligands increases while the catalyst stability increases with increasing amounts of ligand. Therefore, there exists an optimum concentration of phosphorus ligands for operating an oxo reactor which is the result of a tradeoff between increased stability and reduced catalyst activity. 
     In reality, the gradual loss of phosphorus ligands is inevitable because of decomposition and other reasons. In some cases, such as overflow reactors, the decomposition of ligands may be worsened due to the high temperature required to separate catalysts from products. In practice, fresh phosphorus ligands have to be replenished to the reactor on a regular basis to compensate for the loss of ligands. 
     Thus, there is a need in the art for ligands that not only stabilize the catalyst at higher concentrations, but also can increase the catalyst activity at such concentrations. 
     SUMMARY OF THE INVENTION 
     A class of ligands has been discovered that can substantially increase the Rh catalyst activity by simply increasing the novel phosphonite ligand concentration. In some embodiments, the ligand offers one or more benefits such as enhanced catalyst stability, increased production rate, and reduced daily operation costs due to eliminated needs for replenishing ligands. 
     In one aspect, the present invention provides a phosphonite compound having the structure of formula (I): 
                                
wherein
 
     R is an alkyl or aryl group containing 1 to 30 carbon atoms; 
     Ar 1  and Ar 2  are each independently aryl groups containing 4 to 30 carbon atoms; 
     R1 to R6 are each independently selected from H and hydrocarbyl containing 1 to 40 carbon atoms; and 
     X is
         (i) a chemical bond directly between ring carbon atoms of each aromatic group,   (ii) a heteroatom, or   (iii) a group having the formula       

                                
wherein R15 and R16 are each independently selected from hydrogen and alkyl or aryl having up to 10 carbon atoms.
 
     In a second aspect, the present invention provides a catalyst solution comprising: 
     (a) a phosphonite compound; 
     (b) a Group VIII metal or rhenium; and 
     (c) a hydroformylation solvent, 
     wherein the phosphonite compound has the structure of formula (I): 
                                
wherein
 
     R is an alkyl or aryl group containing 1 to 30 carbon atoms; 
     Ar 1  and Ar 2  are each independently aryl groups containing 4 to 30 carbon atoms; 
     R1 to R6 are each independently selected from H and hydrocarbyl containing 1 to 40 carbon atoms; and 
     X is
         (i) a chemical bond directly between ring carbon atoms of each aromatic group,   (ii) a heteroatom, or   (iii) a group having the formula       

                                
wherein R15 and R16 are each independently selected from hydrogen and alkyl or aryl having up to 10 carbon atoms.
 
     In a third aspect, the present invention provides a process for preparing aldehydes, comprising contacting an olefin with hydrogen and carbon monoxide, under hydroformylation conditions, in the presence of the catalyst solution herein described. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     New phosphonite compounds have been discovered that are useful as ligands in hydroformylation reactions. The invention thus provides new phosphonite compounds. The invention further provides highly active catalyst solution for use in hydroformylation reactions. 
     The catalyst solution comprises: 
     (a) a phosphonite compound; 
     (b) a Group VIII metal or rhenium; and 
     (c) a hydroformylation solvent. 
     The phosphonite compound according to the invention has the structure of formula (I): 
                                
wherein
 
     R is an alkyl or aryl group containing 1 to 30 carbon atoms; 
     Ar 1  and Ar 2  are each independently aryl groups containing 4 to 30 carbon atoms; 
     R1 to R6 are each independently selected from H and hydrocarbyl containing 1 to 40 carbon atoms; and 
     X is
         (i) a chemical bond directly between ring carbon atoms of each aromatic group,   (ii) a heteroatom, or   (iii) a group having the formula       

                                
wherein R15 and R16 are each independently selected from hydrogen and alkyl or aryl groups having up to 10 carbon atoms. In some embodiments, R15 and R16 are each independently selected from hydrogen and alkyl groups having one or two carbon atoms. In some embodiments, R15 and R16 are each independently selected from hydrogen and methyl groups.
 
     The heteroatom can be any atom other than carbon that can form the bonds with the two aryl rings as shown in Formula (I) without compromising the efficacy of the ligand. In some embodiments, the heteroatom is selected from sulfur, oxygen, nitrogen, and silicon, provided that the silicon and nitrogen will have additional substituents bonded thereto to complete the atoms bonding capability. Substituents which are acceptable include alkyl groups of 1 to 20 carbon atoms and aromatic groups of 6 to 20 carbon atoms. In some embodiments, the heteroatom is selected from O, Si, and N, again, with additional atoms bonded to a Si or N. 
     R is a hydrocarbyl group selected from unsubstituted and substituted alkyl, cycloalkyl, and aryl groups containing 1 to about 30 carbon atoms. In some embodiments the total carbon content of R is in the range of about 1 to 20 carbon atoms. Examples of the alkyl groups that R can represent include methyl, ethyl, butyl, pentyl, hexyl, 2-ethylhexyl, octyl, decyl, dodecyl, octadecyl and various isomers thereof. The alkyl groups may be substituted, for example, with up to two substituents such as alkoxy, cycloalkoxy, formyl, alkanoyl, cycloalkyl, aryl, aryloxy, aroyl, carboxyl, carboxylate salts, alkoxycarbonyl, alkanoyloxy, cyano, sulfonic acid, sulfonate salts, and the like. Cyclopentyl, cyclohexyl and cycloheptyl are examples of the cycloalkyl groups that R can represent. The cycloalkyl groups may be substituted with alkyl or any of the substituents described with respect to the possible substituted alkyl groups. In some embodiments, the unsubstituted or substituted alkyl and cycloalkyl groups that R can represent are alkyls of up to about 8 carbon atoms, benzyl, cyclopentyl, cyclohexyl, and cycloheptyl. 
     Examples of the aryl groups that R can represent include carbocyclic aryls such as phenyl, naphthyl, anthracenyl, and substituted derivatives thereof. Examples of the carbocyclic aryl groups that R can represent include the radicals having the formulas (II) to (IV): 
                                
wherein R7 and R8 may represent one or more substituents independently selected from alkyl, alkoxy, halogen, cycloalkoxy, formyl, alkanoyl, cycloalkyl, aryl, aryloxy, aroyl, carboxyl, carboxylate salts, alkoxy-carbonyl, alkanoyloxy, cyano, sulfonic acid, sulfonate salts, and the like. In some embodiments, the alkyl moiety of the aforesaid alkyl, alkoxy, alkanoyl, alkoxycarbonyl, and alkanoyloxy groups contains up to about 8 carbon atoms. Although it is possible for m to represent 0 to 5 and for n to represent 0 to 7, the value of each of m and n will not exceed 2. In some embodiments, R7 and R8 represent lower alkyl groups, i.e., straight-chain and branched-chain alkyl of up to about 4 carbon atoms, and m and n each represent 0, 1, or 2.
 
     Optionally, the hydrocarbyl groups represented by R can be selected from unsubstituted and substituted divalent alkylidene, cycloalkylidene, and arylidene groups containing up to about 30 carbon atoms. Examples of such divalent hydrocarbyl groups include, but are not limited to, methylidene, ethylidene, 1,3-propylidene, 1,4-butylidene, 1,5-pentylidene, 1,6-hexylidene, 1,7-heptylidene, 1,8-octyllidene, cyclohexylidene, cyclopentylidene, norbornylidene, biphenyldiyl, methylidenebis(2-phenyl), etc. 
     The hydrocarbyl groups represented by R1 to R4 are selected from unsubstituted and substituted alkyl, cycloalkyl, and aryl groups containing up to about 40 carbon atoms. In some embodiments, the total carbon content of R1 to R4 is in the range of about 1 to 15 carbon atoms. Examples of the alkyl groups that R1 to R4 can represent include methyl, ethyl, butyl, pentyl, hexyl, 2-ethylhexyl, octyl, decyl, dodecyl, octadecyl, and various isomers thereof. The alkyl groups may be substituted, for example, with up to two substituents such as alkoxy, cycloalkoxy, formyl, alkanoyl, cycloalkyl, aryl, aryloxy, aroyl, carboxyl, carboxylate salts, alkoxycarbonyl, alkanoyloxy, cyano, sulfonic acid, sulfonate salts, and the like. Cyclopentyl, cyclohexyl, and cycloheptyl are examples of the cycloalkyl groups that R1 to R4 can represent. The cycloalkyl groups may be substituted with alkyl or any of the substituents described with respect to the possible substituted alkyl groups. In some embodiments, the unsubstituted or substituted alkyl and cycloalkyl groups that R1 to R4 can represent are alkyls of up to about 8 carbon atoms, benzyl, cyclopentyl, cyclohexyl, and cycloheptyl. 
     Examples of the aryl groups that R1 to R4 can represent include carbocyclic aryl such as phenyl, naphthyl, anthracenyl, and substituted derivatives thereof. Examples of the carbocyclic aryl groups that R1 to R4 can represent include radicals having the formulas (V)-(VII): 
                                
wherein R9 and R10 may represent one or more substituents independently selected from alkyl, alkoxy, halogen, cycloalkoxy, formyl, alkanoyl, cycloalkyl, aryl, aryloxy, aroyl, carboxyl, carboxylate salts, alkoxy-carbonyl, alkanoyloxy, cyano, sulfonic acid, sulfonate salts, and the like. In some embodiments, the alkyl moiety of the aforesaid alkyl, alkoxy, alkanoyl, alkoxycarbonyl, and alkanoyloxy groups contains up to about 8 carbon atoms. Although it is possible for p to represent 0 to 5 and for q to represent 0 to 7, in some embodiments, the value of each of p and q will not exceed 2. In some embodiments, R9 and R10 represent lower alkyl groups, i.e., straight-chain and branched-chain alkyl of up to about 4 carbon atoms, and m and n each represent 0, 1, or 2.
 
     The hydrocarbyl groups represented by R5 and R6 may be the same or different, separate or combined, and are selected from unsubstituted and substituted alkyl, cycloalkyl, and aryl groups containing a total of up to about 40 carbon atoms. In some embodiments, the total carbon content of substituents R5 and R6 is in the range of about 1 to 35 carbon atoms. Examples of the unsubstituted or substituted alkyl groups that R5 and R6 can represent include methyl, ethyl, butyl, pentyl, hexyl, 2-ethylhexyl, octyl, decyl, dodecyl, octadecyl, 1-alkylbenzyl, and various isomers thereof. The alkyl groups may be substituted, for example, with up to two substituents such as alkoxy, cycloalkoxy, formyl, alkanoyl, cycloalkyl, aryl, aryloxy, aroyl, carboxyl, carboxylate salts, alkoxycarbonyl, alkanoyloxy, cyano, sulfonic acid, sulfonate salts, and the like. Cyclopentyl, cyclohexyl, and cycloheptyl are examples of the cycloalkyl groups that R5 and R6 individually can represent. The cycloalkyl groups may be substituted with alkyl or any of the substituents described with respect to the possible substituted alkyl groups. In some embodiments the unsubstituted or substituted alkyl and cycloalkyl groups that R5 and R6 can represent are alkyls of up to about 10 carbon atoms such as benzyl, 1-alkylbenzyl, cyclopentyl, cyclohexyl, and cycloheptyl, etc. 
     Examples of the aryl groups that R5 and R6 can represent include carbocyclic aryl such as phenyl, naphthyl, anthracenyl, and substituted derivatives thereof. Examples of the carbocyclic aryl groups that R5 and R5 can represent include radicals having the formulas (VIII)-(X): 
                                
wherein R11 and R12 may represent one or more substituents independently selected from alkyl, alkoxy, halogen, cycloalkoxy, formyl, alkanoyl, cycloalkyl, aryl, aryloxy, aroyl, carboxyl, carboxylate salts, alkoxy-carbonyl, alkanoyloxy, cyano, sulfonic acid, sulfonate salts, and the like. In some embodiments, the alkyl moiety of the aforesaid alkyl, alkoxy, alkanoyl, alkoxycarbonyl, and alkanoyloxy groups contains up to about 8 carbon atoms. Although it is possible for r to represent 0 to 5 and for s to represent 0 to 7, in some embodiments, the value of each of r and s will not exceed 2. In some embodiments, R11 and R12 represent lower alkyl groups, i.e., straight-chain and branched-chain alkyl of up to about 10 carbon atoms, and r and s each represent 0, 1, or 2.
 
     In some embodiments, R1 to R6 in combination or collectively may represent a divalent hydrocarbyl group containing up to about 40 carbon atoms. In some embodiments, the divalent hydrocarbyl group contains from about 12 to 36 carbon atoms. Examples of such divalent groups include alkyl of about 2 to 12 carbon atoms, cyclohexyl, and aryl. Specific examples of the alkyl and cycloalkyl groups include ethylene, trimethylene, 1,3-butanediyl, 2,2-dimethyl-1,3-propanediyl, 1,1,2-triphenylethanediyl, 2,2,4-trimethyl-1,3-pentanediyl, 1,2-cyclohexylene, and the like. 
     Examples of the aryl groups that Ar 1  and Ar 2  can individually represent include carbocyclic aryl such as phenyl, naphthyl, anthracenyl, and substituted derivatives thereof. Examples of the carbocyclic aryl groups that Ar 1  and Ar 2  can represent include radicals having the formulas (XI) to (XIII): 
                                
wherein R13 and R14 may represent one or more substituents independently selected from alkyl, alkoxy, halogen, cycloalkoxy, formyl, alkanoyl, cycloalkyl, aryl, aryloxy, aroyl, carboxyl, carboxylate salts, alkoxy-carbonyl, alkanoyloxy, cyano, sulfonic acid, sulfonate salts, and the like. In some embodiments, the alkyl moiety of the aforesaid alkyl, alkoxy, alkanoyl, alkoxycarbonyl, and alkanoyloxy groups contains up to about 8 carbon atoms. Although it is possible for x to represent 0 to 5 and for y to represent 0 to 7, in some embodiments, the value of each of x and y will not exceed 2. In some embodiments, R13 and R14 represent lower alkyl groups, i.e., straight-chain and branched-chain alkyl of up to about 10 carbon atoms, and x and y each represent 0, 1, or 2. In some embodiments, R13 and R14 represent lower alkyl groups, i.e., straight-chain and branched-chain alkyl of up to about 4 carbon atoms, and x and y each represent 0, 1, or 2.
 
     The phosphonite compounds of this invention can be prepared by any effective method. A variety of methods for preparing phosphonites are reported in “A Guide to Organophosphorus Chemistry”, Louis D. Quin, 2000, Wiley-Interscience, pp. 62 et seq. In general, phosphonites can be prepared by methods similar to those used for preparing phosphites. Examples reported by P. G. Pringle (Chem. Comm., 2000, 961) are effective. 
     The novel catalyst systems provided by the present invention comprise a combination of one or more transition metals selected from the Group VIII metals and rhenium and one or more of the phosphonite compounds described in detail hereinabove. The transition metal may be provided in the form of various metal compounds such as carboxylate salts of the transition metal. In some embodiments, the metal is rhodium. 
     Rhodium compounds that may be used as a source of rhodium for the active catalyst include rhodium (II) or rhodium (III) salts of carboxylic acids, examples of which include di-rhodium tetraacetate dihydrate, rhodium(II) acetate, rhodium(II) isobutyrate, rhodium(II) 2-ethylhexanoate, rhodium(II) benzoate, and rhodium(II) octanoate. Also, rhodium carbonyl species such as Rh 4 (CO) 12 , Rh 6 (CO) 16 , and rhodium(I) acetylacetonate dicarbonyl may be suitable rhodium feeds. Additionally, rhodium organophosphine complexes such as tris(triphenylphosphine)rhodium carbonyl hydride may be used when the phosphine moieties of the complex fed are easily displaced by the phosphonite ligands of the present invention. Other rhodium sources include rhodium salts of strong mineral acids such as chlorides, bromides, nitrates, sulfates, phosphates, and the like. 
     The absolute concentration of rhodium in the reaction mixture or solution may vary from 1 mg/liter up to 5000 mg/liter or more. In some embodiments of this invention, the normal concentration of rhodium in the reaction solution is in the range of about 20 to 300 mg/liter. Concentrations of rhodium lower than this range generally yield lower reaction rates with most olefin reactants and/or require reactor operating temperatures that are so high as to be detrimental to catalyst stability. Concentrations above this range involve higher rhodium costs. 
     The ratio of gram moles phosphonite ligand to gram atoms transition metal can vary over a wide range, e.g., gram mole phosphonite:gram atom transition metal ratio of about 1:1 to 500:1. For rhodium-containing catalyst systems, the gram mole phosphonite:gram atom rhodium ratio in some embodiments is in the range of about 1:1 to 200:1 with ratios in some embodiments in the range of about 1:1 to 100:1. 
     No special or unusual techniques are required for preparing the catalyst systems and solutions of the present invention, although in some embodiments a catalyst of high activity is obtained if all manipulations of the rhodium and phosphonite ligand components are carried out under an inert atmosphere, e.g., nitrogen, argon, and the like. The desired quantities of a suitable rhodium compound and ligand are charged to the reactor in a suitable solvent. The sequence in which the various catalyst components or reactants are charged to the reactor is not critical. 
     The hydroformylation reaction solvent may be selected from a wide variety of compounds, mixture of compounds, or materials that are liquid at the pressure at which the process is being operated. Such compounds and materials include various alkanes, cycloalkanes, alkenes, cycloalkenes, carbocyclic aromatic compounds, alcohols, esters, ketones, acetals, ethers, and water. Specific examples of such solvents include alkane and cycloalkanes such as dodecane, decalin, octane, iso-octane mixtures, cyclohexane, cyclooctane, cyclododecane, methylcyclohexane; aromatic hydrocarbons such as benzene, toluene, xylene isomers, tetralin, cumene, alkyl-substituted aromatic compounds such as the isomers of diisopropylbenzene, triisopropylbenzene and tert-butylbenzene; alkenes and cycloalkenes such as 1,7-octadiene, dicyclopentadiene, 1,5-cyclooctadiene, octene-1, octene-2,4-vinylcyclohexene, cyclohexene, 1,5,9-cyclododecatriene, 1-pentene; crude hydrocarbon mixtures such as naphtha, mineral oils and kerosene; and high-boiling esters such as 2,2,4-trimethyl-1,3-pentanediol diisobutyrate. The aldehyde product of the hydroformylation process may also be used. 
     In some embodiments, the solvent is the higher boiling by-products that are naturally formed during the process of the hydroformylation reaction and the subsequent steps, e.g., distillations, that may be required for aldehyde product isolation. The main criterion for the solvent is that it dissolves the catalyst and olefin substrate and does not act as a poison to the catalyst. Some examples of solvents for the production of volatile aldehydes, e.g., butyraldehydes, are those that are sufficiently high boiling to remain, for the most part, in a gas sparged reactor. Some examples of solvents and solvent combinations that are in the production of less volatile and non-volatile aldehyde products include 1-methyl-2-pyrrolidinone, dimethyl-formamide, perfluorinated solvents such as perfluoro-kerosene, sulfolane, water, and high boiling hydrocarbon liquids as well as combinations of these solvents. Non-hydroxylic compounds, in general, and hydrocarbons, in particular, may be used advantageously as the hydroformylation solvent since their use can minimize decomposition of the phosphonite ligands. 
     In another aspect, the present invention provides a process for preparing aldehydes, comprising contacting an olefin with hydrogen and carbon monoxide, under hydroformylation conditions, in the presence of the catalyst solution herein described. 
     The reaction conditions for the process of the present invention can be conventional hydroformylation conditions. The process may be carried out at temperatures in the range of about 20° to 200° C., in some embodiments, the hydroformylation reaction temperatures are from 50° to 135° C. In some embodiments, reaction temperatures range from 75° to 125° C. Higher reactor temperatures can increase the rate of catalyst decomposition while lower reactor temperatures can result in relatively slow reaction rates. The total reaction pressure may range from about ambient or atmospheric up to 70 bars absolute (about 1000 psig). In some embodiments, pressure ranges from about 8 to 28 bars absolute (about 100 to 400 psig). 
     The hydrogen:carbon monoxide mole ratio in the reactor likewise may vary considerably ranging from 10:1 to 1:10, and the sum of the absolute partial pressures of hydrogen and carbon monoxide may range from 0.3 to 36 bars absolute. The partial pressures of the ratio of the hydrogen to carbon monoxide in the feed can be selected according to the linear:branched isomer ratio desired. Generally, the partial pressure of hydrogen and carbon monoxide in the reactor can be maintained within the range of about 1.4 to 13.8 bars absolute (about 20 to 200 psia) for each gas. The partial pressure of carbon monoxide in the reactor can be maintained within the range of about 1.4 to 13.8 bars absolute (about 20 to 200 psia) and can be varied independently of the hydrogen partial pressure. The molar ratio of hydrogen to carbon monoxide can be varied widely within these partial pressure ranges for the hydrogen and carbon monoxide. The ratios of hydrogen-to-carbon monoxide and the partial pressure of each in the synthesis gas (syn gas—carbon monoxide and hydrogen) can be readily changed by the addition of either hydrogen or carbon monoxide to the syn gas stream. With the phosphonite ligands described herein, the ratio of linear to branched products can be varied widely by changing the partial pressures of the carbon monoxide in the reactor. 
     Any of the known hydroformylation reactor designs or configurations such as overflow reactors and vapor take-off reactors may be used in carrying out the process provided by the present invention. Thus, a gas-sparged, vapor take-off reactor design as disclosed in the examples set forth herein may be used. In this mode of operation, the catalyst which is dissolved in a high boiling organic solvent under pressure does not leave the reaction zone with the aldehyde product taken overhead by the unreacted gases. The overhead gases then are chilled in a vapor/liquid separator to liquefy the aldehyde product and the gases can be recycled to the reactor. The liquid product is let down to atmospheric pressure for separation and purification by conventional technique. The process also may be practiced in a batchwise manner by contacting the olefin, hydrogen and carbon monoxide with the present catalyst in an autoclave. 
     A reactor design where catalyst and feedstock are pumped into a reactor and allowed to overflow with product aldehyde, i.e. liquid overflow reactor design, is also suitable. For example, high boiling aldehyde products such as nonyl aldehydes may be prepared in a continuous manner with the aldehyde product being removed from the reactor zone as a liquid in combination with the catalyst. The aldehyde product may be separated from the catalyst by conventional means such as by distillation or extraction, and the catalyst then recycled back to the reactor. Water soluble aldehyde products, such as hydroxy butyraldehyde products obtained by the hydroformylation of allyl alcohol, can be separated from the catalyst by extraction techniques. A trickle-bed reactor design is also suitable for this process. It will be apparent to those skilled in the art that other reactor schemes may be used with this invention. 
     The olefin used as the starting material for this invention is not particularly limiting. Specifically, the olefin can be ethylene, propylene, butene, pentene, hexene, octene, styrene, non-conjugated dienes such as 1,5-hexadiene, and blends of these olefins. Furthermore, the olefin may be substituted with functional groups so long as they do not interfere with the hydroformylation reaction. Suitable substituents on the olefin include any functional group that does not interfere with the hydroformylation reaction and includes groups such as carboxylic acids and derivatives thereof such as esters and amides, alcohols, nitrites, and ethers. Examples of substituted olefins include esters such as methyl acrylate or methyl oleate, alcohols such as allyl alcohol and 1-hydroxy-2,7-octadiene, and nitriles such as acrylonitrile. 
     The amount of olefin present in the reaction mixture can also vary. For example, relatively high-boiling olefins such as 1-octene may function both as the olefin reactant and the process solvent. In the hydroformylation of a gaseous olefin feedstock such as propylene, the partial pressures in the vapor space in the reactor in some embodiments are in the range of about 0.07 to 35 bars absolute. The rate of reaction can be favored by high concentrations of olefin in the reactor. In the hydroformylation of propylene, the partial pressure of propylene in some embodiments is greater than 1.4 bars, e.g., from about 1.4 to 10 bars absolute. In the case of ethylene hydroformylation, the partial pressure of ethylene in the reactor in some embodiments is greater than 0.14 bars absolute. 
     This invention can be further illustrated by the following examples of embodiments thereof, although it will be understood that these examples are included merely for purposes of illustration and are not intended to limit the scope of the invention. Unless otherwise indicated, all percentages are by weight. As used throughout this application, the reference to a molecule or moiety as being “substituted” means that the molecule or moiety contains one or more substituent in place of where a hydrogen atom would be on the molecule or moiety identified. Thus, a “substituted” aryl molecule having alkyl substituents would include, for example, an alkylbenzene such as toluene. 
     EXAMPLES 
     Synthesis of Phosphonite Ligands 
     Phosphonites were synthesized by reaction of phenyldicholorophosphine or alkyldicholorophosphine with corresponding substituted methylene bisphenols in the presence of triethylamine. All of the syntheses were carried out under nitrogen. 
     A typical procedure follows: 
     Methylene bisphenol (20 mmol) was mixed with triethylamine (44 mmol) in a mixed solvent (toluene:cyclohexane 2:1) and stirred. An ice-bath was applied to maintain the reaction temperature below 5° C. Then, a solution of phenyldicholorophosphine or alkyldicholorophosphine (20 mmol) in toluene (20 to 40 ml) was added slowly into the reaction mixture. After addition, the reaction was continued at 5° C. or lower for 30 min., then the temperature was raised to ambient temperature for 1 hour. The reaction was heated to 50° C. for 6 to 10 hours until complete disappearance of the starting bisphenol as shown by GC analysis. The precipitate that formed was removed by filtration, and the aqueous reaction mixture was washed with water (2×20 ml) and brine (2×20 ml). The organic phase was dried with anhydrous sodium sulfate. The solvents were removed under vacuum to afford the phosphonite compounds. All of these compounds are very soluble in common organic solvents such as diethyl ether, THF, toluene, ethyl acetate, chloroform, etc. Reaction yields are often greater than 85%. They can be purified either by recrystallization (methanol/toluene mixture), distillation, or column chromatography. 
     Ligand A 
     Ligand A, having the structure shown below, was synthesized using 2,2′-methylene bis(6-phenylphenol) with phenyldicholorophosphine. 
     
       
                 
         
             
             
         
      
     
     Ligand “A”: O,O-2,2′-methylene bis(6-phenylphenyl)phenylphosphonite, white crystals. 
     Spectroscopic data of Ligand A: 
       31 P NMR (CDCl 3 ): 168.7 ppm (s).  1 H NMR (CDCl 3 ): 3.65 (d, 1H), 4.61-4.65 (dd, 1H), 6.91-6.95 (m, 2H), 7.13-7.49 (m, 19H) ppm. 
     Ligand B 
     Ligand B, having the structure shown below, was synthesized using 2,2′-methylene bis(4,6-di(α,α-dimethylbenzyl)phenol) with phenyldicholorophosphine. 
     
       
                 
         
             
             
         
      
     
     Ligand “B”: O,O-2,2′-methylene bis(4,6-bis(α,α′-dimethylbenzyl)phenyl)phenylphosphonite, white solid. 
     Spectroscopic data of Ligand B: 
       31 P NMR (CDCl 3 ): 162.2 ppm (s).  1 H NMR (CDCl 3 ): 1.33 (s, 6H), 1.39 (s, 6H), 1.68 (s, 12H), 3.23 (d, 1H), 4.23 (dd, 1H), 6.72 (m, 4H), 6.93-7.30) (m, 20H) ppm. 
     Ligand C 
     Ligand C, having the structure shown below, was synthesized using 2,2′-methylene bis(4,6-di(α,α-dimethylbenzyl)phenol) with cyclohexyldicholorophosphine. 
     
       
                 
         
             
             
         
      
     
     Ligand “C”: O,O-2,2′-methylene bis(4,6-bis(α,α′-dimethylbenzyl)phenyl)cyclohexylphosphonite, white solid. 
     Spectroscopic data of Ligand C: 
       31 P NMR (CDCl 3 ): 189.3 ppm (s).  1 H NMR (CDCl 3 ): 0.61-1.02 (m, 6H), 1.25 (m, 2H), 1.47-1.55 (m, 15H), 1.66 (s, 12H), 3.14 (d, 1H), 3.99-4.03 (dd, 1H), 7.03-7.27 (m, 24H) ppm. 
     Ligand D 
     Ligand D, having the structure shown below, was synthesized using 2,2′-methylene bis(4,6-di(α,α-dimethylbenzyl)phenol) with methyldicholorophosphine. 
     
       
                 
         
             
             
         
      
     
     Ligand “D”: O,O′-2,2′-methylene bis(4,6-bis(α,α′-dimethylbenzyl)phenyl)methylphosphonite, white solid. 
     Spectroscopic data of Ligand D: 
       31 P NMR (CDCl 3 ): 190.6 ppm (s).  1 H NMR (CDCl 3 ): 0.39 (d, 3H), 1.36 (s, 6H), 1.57 (s, 6H), 1.68 (s, 12H), 3.15 (d, 1H), 3.99-4.03 (dd, 1H), 7.00-7.29 (m, 24H) ppm. 
     Hydroformylation Process Set-Up 
     The hydroformylation process in which propylene is allowed to react with hydrogen and carbon monoxide to produce butyraldehydes was carried out in a vapor take-off reactor made up of a vertically arranged stainless steel pipe having a 2.5 cm inside diameter and a length of 1.2 meters. The reactor was encased in an external jacket that was connected to a hot oil machine. The reactor has a filter element welded into the side down near the bottom of the reactor for the inlet of gaseous reactants. The reactor contained a thermocouple which was arranged axially with the reactor in its center for accurate measurement of the temperature of the hydroformylation reaction mixture. The bottom of the reactor has a high pressure tubing connection that was connected to a cross. One of the connections to the cross permitted the addition of non-gaseous reactants such as higher boiling alkenes or make-up solvents, another led to the high-pressure connection of a differential pressure (D/P) cell that was used to measure catalyst level in the reactor and the bottom connection was used for draining the catalyst solution at the end of the run. 
     In the hydroformylation of propylene in a vapor take-off mode of operation, the hydroformylation reaction mixture or solution containing the catalyst was sparged under pressure with the incoming reactants of propylene, hydrogen and carbon monoxide as well as any inert feed such as nitrogen. As butyraldehyde was formed in the catalyst solution, it and unreacted reactant gases were removed as a vapor from the top of the reactor by a side-port. The vapor removed was chilled in a high-pressure separator where the butyraldehyde product was condensed along with some of the unreacted propylene. The uncondensed gases were let down to atmospheric pressure via the pressure control valve. These gases passed through a series of dry-ice traps where any other aldehyde product was collected. The product from the high-pressure separator was combined with that of the traps, and was subsequently weighed and analyzed by standard gas/liquid phase chromatography (GC/LC) techniques for the net weight and normal/iso ratio of the butyraldehyde product. 
     The gaseous feeds to the reactor were fed to the reactor via twin cylinder manifolds and high-pressure regulators. The hydrogen passed through a mass flow controller and then through a commercially available “Deoxo” (registered trademark of Englehard Inc.) catalyst bed to remove any oxygen contamination. The carbon monoxide passed through an iron carbonyl removal bed (as disclosed in U.S. Pat. No. 4,608,239), a similar “Deoxo” bed heated to 125° C., and then a mass flow controller. Nitrogen can be added to the feed mixture as an inert gas. Nitrogen, when added, was metered in and then mixed with the hydrogen feed prior to the hydrogen Deoxo bed. Propylene was fed to the reactor from feed tanks that were pressurized with hydrogen and was controlled using a liquid mass flow meter. All gases and propylene were passed through a preheater to ensure complete vaporization of the liquid propylene prior to entering the reactor. 
     Comparative Examples 1-3 
     Fluorophosphite Ligand 
     Comparative Examples 1-3 were taken directly from Puckette, “Catalysis of Organic Reactions”, Edited by S. R. Schmidt, CRC Press (2006), pp. 31-38, to illustrate that hydroformylation activity decreases as the molar ratio of ligand to Rh increases (the concentration of ligand increases). The ligand described in this literature is a fluorophosphite (Ethanox 398™, 2,2′-ethylidenebis(4,6-di-tert-butylphenyl)fluorophosphite). 
     According to the literature, the reactions were conducted at 260 psig, 115° C., 1:1 H2/CO, 54 psia C 3 H 6 , and 190 mL of bis-2-ethylhexylphthalate solvent (DOP) with different amounts of ligand. The data is presented in Table 1 below and catalyst activity is expressed as kilograms of butyraldehyde per gram Rh per hour. 
     Comparative Examples 4-6 
     Ligand A 
     These examples illustrate that a non-preferred, regular phenylphosphite (Ligand A) also shows a typical relationship between hydroformylation activity and the molar ratio of ligand to Rh, i.e., the aldehydes production rate decreases as the ligand concentration increases. 
     A catalyst solution was prepared under nitrogen using a charge of 7.5 mg of rhodium (0.075 mmol, as rhodium 2-ethylhexanoate); various amounts of Ligand “A” as indicated in Table 1; 20 ml of normal butyraldehyde; and 190 ml of bis-2-ethylhexylphthalate(dioctylphthalate, DOP). The mixture was stirred under nitrogen until a homogeneous solution was obtained (heated if necessary). 
     The mixture was charged to the reactor in a manner described previously and the reactor sealed. The reactor pressure control was set at 17.9 bar (260 psig), and the external oil jacket on the reactor was heated to 85° C. Hydrogen, carbon monoxide, nitrogen, and propylene vapors were fed through the frit at the base of the reactor, and the reactor was allowed to build pressure. The hydrogen and carbon monoxide (H2/CO ratio was set to be 1:1) were fed to the reactor at a rate of 6.8 liters/min and the nitrogen feed was set at 1.0 liter/min. The propylene was metered as a liquid and fed at a rate of 1.89 liters/min (212 grams/hour). The temperature of the external oil was modified to maintain an internal reactor temperature of 85° C. The unit was operated for 5 hours and hourly samples taken. The hourly samples were analyzed as described above using a standard GC method. The last three samples were used to determine the N/I ratio and catalyst activity. 
     The reaction conditions and the results of this work are presented in Table 1. 
     Examples 7-11 
     Ligand B 
     These examples illustrate a desirable nature of phosphonite Ligand B. 
     Hydroformylation experiments were carried out in the same manner as Comparative Examples 4-6, except utilizing various amounts of Ligand “B”. The reaction conditions and the results of this work are presented in Table 1. 
     Examples 12-13 
     Ligand C 
     These examples illustrate a desirable nature of phosphonite Ligand C. 
     Hydroformylation experiments were carried out in the same manner as Comparative Examples 4-6, except utilizing various amounts of Ligand “C”. The reaction conditions and the results of this work are presented in Table 1. 
     Examples 14 to 16 
     Ligand D 
     These examples illustrate a desirable nature of phosphonite Ligand D. 
     Hydroformylation experiments were carried out in the same manner as Comparative Examples 4-6, except utilizing various amounts of Ligand “D”. The reaction conditions and the results of this work are presented in Table 1. 
     
       
         
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Effects of Ligand to Rhodium Molar Ratio on Activity and 
               
               
                 Selectivity 
               
             
          
           
               
                   
                   
                   
                   
                 Ligand 
                   
                   
               
               
                   
                   
                   
                   
                 to Rh 
               
               
                 Example 
                   
                 Temp 
                 H2/CO 
                 Molar 
                 N/I 
                 Catalyst 
               
               
                 No. 
                 Ligand 
                 (° C.) 
                 ratio 
                 ratio 
                 Ratio 
                 Activity* 
               
               
                   
               
             
          
           
               
                 C-1 
                 fluorophosphite 
                 115 
                 1:1 
                 14:1 
                 1.4 
                 15.7 
               
               
                 C-2 
                 fluorophosphite 
                 115 
                 1:1 
                 30:1 
                 3.1 
                 6.6 
               
               
                 C-3 
                 fluorophosphite 
                 115 
                 1:1 
                 50:1 
                 3.8 
                 3.3 
               
               
                 C-4 
                 A 
                 95 
                 1:1 
                 15:1 
                 1.70 
                 11.70 
               
               
                 C-5 
                 A 
                 95 
                 1:1 
                 30:1 
                 2.25 
                 4.25 
               
               
                 C-6 
                 A 
                 95 
                 1:1 
                 60:1 
                 2.40 
                 3.87 
               
               
                 7 
                 B 
                 85 
                 1:1 
                 15:1 
                 2.09 
                 1.80 
               
               
                 8 
                 B 
                 85 
                 1:1 
                 30:1 
                 1.92 
                 3.95 
               
               
                 9 
                 B 
                 85 
                 1:1 
                 60:1 
                 1.83 
                 6.41 
               
               
                 10 
                 B 
                 85 
                 1:1 
                 90:1 
                 1.79 
                 8.14 
               
               
                 11 
                 B 
                 85 
                 1:1 
                 180:1  
                 1.76 
                 8.20 
               
               
                 12 
                 C 
                 85 
                 1:1 
                 15:1 
                 2.79 
                 0.19 
               
               
                 13 
                 C 
                 85 
                 1:1 
                 30:1 
                 2.81 
                 0.25 
               
               
                 14 
                 D 
                 95 
                 1:1 
                 15:1 
                 1.53 
                 5.44 
               
               
                 15 
                 D 
                 95 
                 1:1 
                 20:1 
                 1.52 
                 6.68 
               
               
                 16 
                 D 
                 95 
                 1:1 
                 30:1 
                 1.57 
                 7.03 
               
               
                   
               
               
                 *Activity was determined as kilograms of butyraldehydes produced per gram of rhodium per hour. All examples were done using 0.075 mmol of Rh. 
               
             
          
         
       
     
     Comparative Examples 1 through 3 illustrate that the hydroformylation reaction activity, under the same reaction temperature and pressure, steadily decreased from 15.7 to 3.3, and the N/I ratio steadily increased from 1.4 to 3.8 when the Ligand/Rh molar ratio increased from 14:1 to 50:1. 
     Comparative Examples 4 through 6 again illustrate the typical, conventional behavior of a phosphonite ligand. Under the same reaction temperature (95° C.) and pressure, hydroformylation activity steadily decreased from 11.70 to 3.87, and the N/I ratio steadily increased from 1.70 to 2.40 when the Ligand/Rh molar ratio increased from 15:1 to 60:1 
     Examples 7 through 11 illustrate the desirable nature of Ligand “B”. Example 7 showed an activity of 1.80 and an N/I value of 2.09 for a 15:1 Ligand/Rh ratio. As the ratio of Ligand/Rh increased to 60:1 under the same reaction temperature and pressure, the activity increased to 6.41, and the N/I ratio decreased to 1.83 (Example 9). The hydroformylation activity increased to 8.20 even when the Ligand to Rh ratio increased to 180:1 (Example 11). Typically, the hydroformylation reaction would be inactive under such a high Ligand/Rh loading. 
     Examples 12 and 13 illustrate the desirable nature of Ligand “C”. When the Ligand/Rh ratio increased from 15:1 to 30:1, the activity increased from 0.19 to 0.25, and the N/I value increased from 2.79 to 2.81 under the same reaction temperature and pressure. 
     Examples 14 through 16 illustrate the desirable nature of Ligand “D”. When the Ligand/Rh ratio increased from 15:1 to 60:1, the activity increased from 5.44 to 7.03, and the N/I value increased from 1.53 to 1.57 under the same reaction temperature and pressure. 
     The invention has been described in detail with particular reference to preferred embodiments and illustrative examples thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.