Abstract:
A reaction block for mounting various round bottom flasks upon a laboratory, magnetic hot plate stirrer. An aluminum inner flask holder effectively conducts heat and does not interfere with a magnetic flux. A solid heat insulating material substantially surrounds and is spaced from the flask holder, in order to keep the reaction block at a safe temperature and provide easy gripping surface regions that extend completely around its circumference.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a reaction block assembly capable of accommodating round bottom flasks, of different sizes, and is for use upon a magnetic stirrer integrated with a hot plate. Such stirrers generate a magnetic field, and various sizes of round bottom flasks are easily accommodated by this device for effective rotating the magnetic stir bars in the flask. The base of the assembly is aluminum and is configured to provide excellent heat transfer land and not to interfere with the magnetic field, being generated from below the hot plate surface.  
         [0003]     2. Brief Description of the Prior Art  
         [0004]     In the field of organic chemistry it is often desirable to perform a chemical reaction under precise heat transfer and stirring conditions. conditions. Known laboratory stirrers suited for use with the present invention include the Opti CHEM Model CG-1993-01 hot plate stirrer from Chemglass of Vineland NJ; the Ikamag RET, RCT and RH Basic magnetic stirrers from IKA of Germany; and the Heidolph MR3000 series of magnetic stirrers. Typically such hotplates are round and have a diameter of 135 mm, although some hotplate stirrers, such as the Snijders Model 34532, from Snijders of the Netherlands, employ a top plate diameter of 194 mm.  
         [0005]     Magnetic stirrers that do not allow for heating are also known. Wanninger at al. (U.S. Pat. No. 5,547,280) illustrates a stirrer with a round, flat glass top. Other magnetic stirrers without a hotplate employ a 6 inch by 6 inch square top plate, such as the Model 1266 from Labline, or a square 7 inch by 7 inch square top plate, such as the Model S46720, from Thermolyne.  
         [0006]     The use of reaction blocks to hold reaction vessels upon a surface of a magnetic stirrer is known. Landsburger (U.S. Pat. No. 3,356,316) illustrates a vinyl block with a plurality of test tube holders.  
         [0007]     Where both stirring and heating are desired, prior art heat conduction blocks have been constructed of various configurations and materials. Kindmann (U.S. Pat. No. 5,529,391) illustrates thermoelectric elements and metal cooling fins attached to each of four sides of a square, aluminum heat conducting block, that then is positioned over a plurality of individual magnetic stirring devices. Ladlow et al. (U.S. Pat. No. 6,905,656) illustrates a solid adapter block with a plurality sockets to arrange test tubes outside of the periphery of a round hot plate stirrer, wherein the adapter block is said to be made of any chemically resistant material, such as PTFE, aluminum or stainless steel. Asynt, of the United Kingdom, sells a DrySyn aluminum adapter block for supporting a standard 1000 ml flask upon a round hot plate stirrer, with separate inserts available for accommodating 500 ml, 250 ml, 100 ml and 50 ml flasks, wherein two plastic handles are attached to opposing sides of a large aluminum block to allow lifting.  
         [0008]     Such apparatus can overheat a hot plate, due to a large mass of aluminum, are difficult to manipulate and include large exposed surfaces that invite burns from inadvertent contact. The present device is advantageous over such known devices in that it allows a conventional magnetic stirrer to be used with various sizes of common round bottom flasks and features a flask holder with thin walls and a small aluminum mass, except about the center where the excellent heat transfer is concentrated. A heat shield is cooled by natural convection through interconnected narrow air spaces, and is easy and safe to manipulate, even when quickly taking the reaction block off the hot plate.  
       SUMMARY OF THE INVENTION  
       [0009]     A reaction block according to the invention provides a safe and cost effective solution for replacing existing oil baths and heating mantles. An innovative heat shield, preferably of solid Teflon (PTFE resin), substantially surrounds the exterior surfaces of an inner aluminum flask holder, to both provide a substantially continuous gripping surface region and keep the entire exterior surface area at a temperature safe to touch. For example, in the preferred embodiment discussed below, the PTFE shield remained at approximately 79° C. when heating a 100 mL round bottom flask to 179° C. Thereby, various common size flasks, holding a hot liquid and one or more magnetic stir bars, can be accommodated securely in this novel reaction block and the reaction block may be quickly and securely grabbed at any vertical side surface and placed upon, or removed from, a hot plate stirrer.  
         [0010]     The present invention provides an improved reaction block, wherein an inner flask holder is shielded both around the circumference of its vertical sides with an insulating material and also shielded at its outer upper surface by an annular surface of insulating material located between the sides and a central flask holding recess. The shielding preferably is a single piece of solid plastic or resin that is removably secured to the inner flask holder and spaced therefrom by spacers to provide a natural convection air space therebetween.  
         [0011]     The present invention preferably provides the bottom of the inner flask holder with a lip that acts to loosely engage the side surface of a hot plate. This ensures that the reaction block is in good heat transfer contact with the hotplate and also correctly locates the supported flask centrally within the magnetic flux being generated by the magnetic stirring mechanism.  
         [0012]     The inner flask holder preferably is cast, forged or machined from aluminum, but alternatively might be made of any non-ferrous metal, stainless steel, ceramic or other high heat transfer coefficient material that will not interfere with a magnetic flux. The preferred embodiment is an inner flask holder that has a lower surface and lip that are circular in shape, to accommodate the common, round hot plate stirrers, as discussed above, but rectangular, square or any other particular shape is contemplated.  
         [0013]     The preferred embodiment of the improved reaction block illustrated in the drawings comprises an inner flask holder with a central recess that will engage a 100 mL round bottom flask and will accept optional inserts for 10, 25 and 50 mL flasks. A second embodiment, not illustrated, comprises a reaction block with an inner flask holder with a central recess that will engage a 500 mL flask and will accept an optional insert for engaging a 250 mL round bottom flask. Preferably the flask inserts are color coded for easy identification by the lab technician. Each of the inserts preferably are shallow cups, made of aluminum and with a common lower convex surface configuration that will make a large area contact against the concave surface of the central recess in the inner flask holder. The upper concave surfaces of the insets are likewise shaped to make a large area contact with the bottom of a particular size of inserted flask.  
         [0014]     Hence, it is a first object of the present invention to provide a reaction block with an insulating heat shield that substantially surrounds an inner flask holder, to keep the exterior surface area at a temperature that is safe to touch.  
         [0015]     It is a second object of the present invention to provide a reaction block with a plastic or resin covering that substantially surrounds an inner flask holder, and provides gripping surface regions completely around its circumference.  
         [0016]     It is a third object of the present invention to provide a reaction block with an insulating heat shield, that substantially surrounds an inner flask holder which further comprises a concave, central recess that accepts a series of inserts sized to accommodate different round bottom flasks but with convex lower surfaces that will make good heat transfer contact with the central recess.  
         [0017]     It is a fourth object of the present invention to provide a reaction block essentially comprising a round, heat conducting inner flask holder with an air space between outer surfaces thereof and a surrounding layer of insulating material so as to cool, by natural convection, a continuous vertical gripping surface region around the circumference of the device.  
         [0018]     It is a fifth object of the present invention to provide a round reaction block essentially comprising a flask holder at its center and a surrounding layer of solid PTFE resin, wherein the inner flask further comprises a large vertically extending aluminum mass surrounding the central flask holder above a horizontal, thin wall aluminum circular element with a lower surface and vertical edge that will engage upon and around a common round hot plate stirrer.  
         [0019]     It is a sixth object of the present invention to provide a reaction block essentially comprising a round, aluminum inner flask holder with a surrounding layer of insulating material and a central recess that will make good heat transfer contact with a series of aluminum adapters for different size flasks, that also are color coded. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     A preferred embodiment of the invention is described in detail below, with reference to the accompanying drawings, wherein:  
         [0021]      FIG. 1  is a right front perspective, explosion view of a reaction block with an optional 50 ml. flask adapter insert according to a preferred embodiment of my invention, in an intended use upon a laboratory magnetic stirrer hot plate, that is shown in dotted line;  
         [0022]      FIG. 2  is a top plan view of the reaction block of  FIG. 1 ;  
         [0023]      FIG. 3  is a is a bottom plan view of the reaction block of  FIG. 1 ;  
         [0024]      FIG. 4  is a left side elevation view of the reaction block of  FIG. 1 , the right side being a mirror image thereof;  
         [0025]      FIG. 5  is a vertical cross-section view of the reaction block of  FIG. 1 , taken along the line  5 - 5  of  FIG. 2 ; and also in an intended use upon a top surface of a laboratory magnetic stirrer and hotplate, that is shown in dotted line.  
         [0026]      FIG. 6  is a top plan view of a first insert for accommodating a 50 ml round bottom flask.  
         [0027]      FIG. 7  is a top plan view of a second insert for accommodating a 25 ml round bottom flask.  
         [0028]      FIG. 8  is a top plan view of a third insert for accommodating a 10 ml round bottom flask.  
         [0029]      FIG. 9  is a side elevation view of a first insert for accommodating a 50 ml round bottom flask.  
         [0030]      FIG. 10  is a side elevation view of a second insert for accommodating a 25 ml round bottom flask.  
         [0031]      FIG. 11  is a side elevation view of a third insert for accommodating a 10 ml round bottom flask. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]     The preferred embodiment of the improved reaction block illustrated in  FIG. 1  comprises an inner flask holder  2  of machined aluminum with an encircling heat shield  4 . The aluminum flask holder central element  12  has an upper support edge  50 , which surrounds a concave central recess  14 , and is supported above a thin wall, circular horizontal element  22 . The concave central recess  14  is sized to engage the bottom of a 100 mL round bottom flask.  
         [0033]      FIG. 1  illustrates a preferred reaction block with an insulating heat shield that is an annular solid block which substantially surrounds a central mass of an aluminum inner flask holder  2 , in a manner that keeps the exterior surface  32  at a temperature that is safe to touch. A block is preferably of cast or machined rigid Teflon (PTFE) resin  4  and shaped to shield substantially all exterior surfaces of the inner flask holder  2 .  
         [0034]      FIGS. 2 and 3  show top and bottom plan views of the reaction block when assembled.  FIGS. 1 and 5  illustrate how the shield is removably mounted and separated from hot surfaces of the flask holder by three ceramic standoffs  6 , 8 , 10  that are ½ inch in diameter and ⅜ inches in length and are spaced equally upon the horizontal element  22  around the holder central element  12 . The shield is held in place by cap screws  16 ,  18 ,  20  that engage threaded holes  26 ,  28 ,  30  tapped into the top of the thin wall of horizontal element  22  and end at its lower surface  80 . As shown in  FIG. 5 , the cap screw  18  also is countersunk in hole  28  well below the surface  38  in order to avoid a burn from contact with the head of the cap screw.  
         [0035]     Hence, interconnected horizontal and vertical spaces create a natural convection air path. As shown in  FIGS. 2 and 5 , a top vertical air space  58  is defined between PTFE shield upper vertical wall  60  and flask holder top support surface  50 . Likewise, a horizontal air space  56  is defined between thin wall flask holder element  22  and the lower horizontal surface of the PTFE block  4  and a bottom vertical air space  54  is defined between outside of vertical element  24  and PTFE block lower vertical wall  72 . The PTFE block outer surface was found to remain at approximately 79° C. when heating a 100 mL round bottom flask to 179° C. The thin wall horizontal element  22  quickly conducts heat radially inward towards the mass of the central flask holder element  12 , so the aluminum flask holder overall has a minimized amount of mass and thermal capacity. Hence, the improved reaction block quickly responds to changes in temperature being required by the controller (not illustrated) which dictates the temperature at the hot plate surface  70 .  
         [0036]      FIGS. 1, 4  and  5  further illustrate the configuration of a solid PTFE shield that both substantially covers and surrounds all hot surfaces of the hot plate  70  as well as the inner flask holder  2 , and also provides gripping surface regions completely around the circumference  32  of the reaction block. The shield has a thick annular portion with an upper surface  38  that extends inward to a cylindrical inner surface  60  that is closely spaced outwardly from the outside of cylindrical holder element  12 . Hence, shield outer circumference  32  meets upper surface  38  at a chamfered corner and is backed by a thick annular ring of solid PTFE resin. That mass further acts to retard heat transfer away from the hot flask holder  2  or the hot plate  70  and towards the circumference  32 . That surrounding, thick annular layer of insulating material is quite rigid and allows a very stable and continuous gripping surface region to be defined by round grooves  34 ,  36  which act as secure finger holding surfaces that are uniform and run completely around the circumference.  
         [0037]      FIG. 5  further illustrates an intended use of the assembled reaction block upon a top surface of a conventional laboratory magnetic stirrer and hotplate,  62 . The shape of a round hot plate upper surface  70  being about 135 mm in diameter is schematically represented by dotted line. The flat lower surface  80  of the thin wall, circular horizontal element  22  is about 138 mm in diameter and will engage over and around the flat area and edge of hot plate upper surface  70 . The reaction block will be located against sliding by the holder vertical element  34 , which in turn is covered by a PTFE shield. In this manner, the reaction block will remain fixed and centrally located within the magnetic field of the laboratory stirrer, but no hot surface will be exposed for an inadvertent contact with the hands of the lab technician.  
         [0038]     As shown in  FIGS. 1, 6  and  9 , the concave central recess  14 , which is sized for engaging against a 100 ml flask bottom, also will engage against the rim  46  and lower convex surface  44  of an optional first adapter insert, that has an upper concave surface  48  sized to engage the bottom of a 50 mL flask. The upper surface  38  of the PTFE block has a notch  40  that registers radially with a notch  42  in the top support surface  50  of the inner flask holder  2 . That facilitates engaging a tool under the insert rim  46  in order to lift out the insert.  
         [0039]      FIGS. 7 and 10  show a second adapter insert, having an upper concave surface  68  that will engage the bottom of a 50 mL flask, an annular rim  66  and a lower convex surface  64  that likewise will engage central recess  14 .  FIGS. 8 and 11  show a third adapter insert, having an upper concave surface  78  that will engage the bottom of a 10 mL flask, an annular rim  76  and a lower convex surface  74  that likewise will engage central recess  14 .  
         [0040]     The three inserts are machined from aluminum, and preferably are anodized in the different colors red, blue and yellow as a color code to facilitate proper selection in the lab.  
         [0041]     Each of the inserts are shallow cups are of the same overall diameter and with the same sized annular rims, but have different wall thicknesses, in order to present a common lower convex surface configuration that will assist in making a large area contact against the concave surface  14  of the central recess in the inner flask holder. The upper concave surfaces of the insets are likewise shaped to make a large area contact with the bottom of a particular size of inserted flask, and are shallow to permit the lab technician to visually inspect a reaction occurring within the liquid being synthesized without the need to employ a surrounding oil bath or a heating mantle.  
         [0042]     While preferred embodiments have been shown and described in order to satisfy the requirements of 35 USC § 112, the invention is to be defined solely by the scope of the appended claims