how to keep 300dpi resolution when saving a jpeg from illustrator

Hey!
i just faced that issue myself and believe me or not it was the guidelines that kept me from exporting my JPEG. I it took me 2hrs to figure out that i have to hide them so the program doesn't take them into consideration and making the file gigantic.

Edit: this is a really old thread but maybe my solution will help someone 

I don't see a JPEG option under File > Export 

Below is the screenshot

a Wonky Solution for Illustrator NOT exporting jpeg 300dpi:

I have to:

1. export my artowrk in TIFF at 300 dpi, cmyk,

2. open Photoshop, then export my TIFF to jpeg -

This works everytime without issues. Perfect nope but your end result will be a cymk or rgb 300 dpi jpeg. Now only if Adobe would have just gave this as a quick solution... (I got your backs fellow designers)

There is probably a better or more professional way but this is how I do it:

When ready to export your image from Adobe Illustrator

On the artboard, Click on your image to Select

On the Navigation Bar click Object and select Rasterize

File > Export

Select JPEG

Name your File

Click Save

On the JPEG Options screen under resolution

Select Depth: Custom from drop down

Enter 300 dpi

Click OK to save your new jpg

Use file >> export >>jpeg>resolution >> custom 300

Sounds like you were using save for web.

As I recall there should be an option for export preferences specifying low--72, medium--150, and high--300dpi.  Someone correct me if I am misremembering.

Object > Rasterize